I switched to using an Apple Macbook Pro about a month ago. What follows is an in-depth review of some of the software I've been using on the Mac.
Positives
Parallels Desktop for Mac OS X is simply amazing. It seems to run Windows better than a Windows PC does. If given enough RAM, it can launch Windows XP in 10 seconds flat! How long does Windows take to boot on your PC, I wonder? You can have Windows running in one Window on the Mac and simply move the mouse into that and use it as you would any other application. You can also set it to rotate the screen between the operating systems with a cube effect: so Windows is running on one side of a cube and Mac OS X on the other. Applications run at almost full speed (although they can only use one of the two processors at a time). No slowdown whatsoever from what I could tell. You can also copy and paste text between the two operating systems. Finally, Windows can access any of the Mac hardware and filesystem (if you let it), even though they are completely different systems (of course, some Mac specific features, such as tracking file creation time, don't work when creating files in the Mac filesystem using Windows). Network connections can either be shared, or the guest operating system can appear as a separate computer. All in all, everything just works. Very nice. Want more info? Ars Technica has posted a very detailed review.
Presentation software: Keynote is an application from Apple for creating jaw dropping presentation. It is much, much (!) better than Powerpoint. Steve Jobs, the Apple CEO, uses it for all his famous presentations. Al Gore used it for his presentation on global warming which was recently made into a feature length film (An Inconvenient Truth). I haven't seen it, but its getting rave reviews and has made $10 million at the box office so far. Pretty good given that the film is basically just a video of Gore giving a Keynote presentation using his Apple notebook computer.
Aside: it is becoming easier and easier to create quality presentations/videos. Now everyone's doing it. For example: Angela Merkel, the new German Chancellor, has just started giving a weekly video podcast. Aim: "Directly addressing the people", "appeal to the youth", etc. etc.
Rosetta emulation is good, but not great. Almost all emulated software runs fine. However, if you attempt to open and edit a Word document that contains lots of images the computer grinds to a halt. Word is otherwise okay to use. There is a very slight, but noticeable delay before every action, but it is still perfectly usable (just not with images in a document). Of course, there are plenty of other word processor alternatives that will also read (and save) Word documents. However, none are however as fully featured / bloated as Word. Grammar checking, for example, is not included in any of them.
The Ecto blog writing software I use is really good. It makes it very easy to write blog entries offline and post them with a touch of a button. You can even include pictures and set them to upload with the main article. Lots of options, lots of features. It does however currently still runs in Rosetta emulation, but you'd never know. It's lightning quick.
Endo is a brilliant little RSS reader. I was previously using Bloglines, but Endo has replace it. It makes reading loads and loads of RSS feeds fast and easy. RSS is different from email. I scan RSS quickly for something that might interest me, while I read and respond to email in detail. Endo allows me eat through loads of feeds in practically no time at all.
Apple's Mail app is great. Fast (really fast), simple and uncluttered, yet can do almost everything that Outlook can. It's spam filter is also quite good. It can learn from what you label as spam or not-spam. Over time it will learn to catch most spam and never label something that isn't spam as such. Some spam will always slip through the net, of course.
iPhoto is a great photo management application. It completely replaces the traditional folder structure for pictures with a much more useful interface. Unlike similar tools on the PC (Photoshop Elements or Picasa), there are lots of plug-ins available that enable you to directly and easily export pictures into online galleries (flickr, coppermine, gallery, etc.). iPhoto can automatically handle all the resizing, re-naming and uploading. Simple.
SuperDuper! is the best backup software I've ever used. I wouldn't have thought that creating a backup is so difficult, but SuperDuper seems to be the only software in the world that that is easy to use and does fast, accurate and smart hard drive synchronization. The process for backing up my 120 GB hard drive is: plug in external hard drive, launch SuperDuper, press the "backup now" button, wait 20 minutes, done (the software only copies the changed files and removes any deleted files). You can, should your computer's hard drive fail, plug in the backup drive, boot the computer via USB and carry-on working, as if nothing had happened. Mac OS X has a special feature that you can seamlessly boot from and use an external drive as the main system drive.
Bonuses
No need for virus checker, anti-spyware tool, or third-party firewall needed. Zero viruses and spyware on the Mac. A good firewall is built into the operating system.
Real plug and play. For example: the process for using a new, unknown printer is: Plug in, press print. No hunting for drivers, no millions of pop-up boxes telling you that the new hardware is being recognized. It just works (Apple has included about 2 GB of common drivers with the OS).
Lots and lots of little things. Every time I've wished: "if only it could do that", I've found that it actually could do that. The Mac platform just oozes with attention to detail.
Negatives
Software sometimes crashes. That will always be there. Nothing disastrous, just annoying. I expect better from Apple! The entire operating system has even hung and/or crashed on me a few times. It seems that Apple is still struggling to get rid of some of the glitches in the new Intel hardware.
Firefox is not as good on the Mac as it is on Windows (not bad, of course, just has a few quirks). There are however plenty of alternative web-browsers: Camino, Safari, Shiira, Opera and Omniweb and (cough) Internet Explorer. You can pick the one that you like best.
Video Skype has not yet materialized. It is definitely being worked on, but no fruits so far.
Synchronization software for Windows Mobile 5 (for my T-mobile MDA Vario smartphone) has also not yet materialized. The two companies (missing sync and pocketmac) that make this kind of software have had about a year to work on it already, but, once again, no fruits as of yet.
Some older hardware does not work. I could not, for example, format my backup drive for the Mac. I had to use a different, older, PowerPC-based Mac computer to do that. Also, my digital camera can't directly connect to the Mac (it can however connect to Windows running in Parallels and, in that round-about way, transfer files). I usually just use an external card reader.
Some relearning required: things work differently on the Mac. Keyboard shortcuts are different (but actually make sense), windows have different buttons, the equivalent of the Windows-explorer is not quite as intuitive. It all takes some getting used to, but is worth it, in the end.