I converted to Mac about 2 years ago, after they switched to Intel architecture.
I used PCs for 12 years as a very HEAVY power user... I've had Dells HPs and computers I've built by myself.
Currently I own a Mac Pro, MacBook Pro, 2 mac minis, an iPod, and (soon) an iPhone.
Reasons I Love my Mac family:
1. high quality components (they don't use crappy hardware) and there is no such thing as a low end machine. every time you buy a new mac, you are getting a top of the line computer.
2. excellent retail experience (if you live close to an Apple store, you HAVE to go check it out)
3. Knowlegable, american based support. I called three times, twice getting their call center in California, only once going to India. This was before I discovered the "genius bar" at the apple store. Now I go in there when I have a question and I get free IN PERSON support.
4. Security. Security against viruses, malware, etc. macs give you Unix security! Amazing!
5. TONS of free software! It's true that not every title is available for Mac, but oftentimes there is a FREE alternative. (i.e. I use Adium for instant messaging, it's far superior to any IM client for PC)
6. Spotlight search eliminates the need for wasting days categorizing and cataloging your files and programs into nerdy little folders. When you want to start something, just hit the spotlight and type it in. It searches inside your documents, mail messages, everything!
7. Superior apps. Particularly iTunes, Mail, and iPhoto are just hands down superior to any other SW out there.
8. Incredibly anal approach to User Interface. It's near perfect, and every detail is thought through excruciatingly.
9. Even more anal approach to design. Backlit keyboard, aluminum case... i could go on and on...
10. Macs love each other on the network... they easily share files, music, etc. I have spent days troubleshooting permissions and sharing from Windoze machines.
For those people who HAVE to run windows... I would recommend using VMWare's Fusion rather than Parallels. It's much more stable, has better performance and compatibility.
For switchers from MS Office: Office '08 for Macs is coming out tomorrow. It will support all your office files. Entourage (the Outlook equivalent) does not support direct import of your .PST file, but there is a supported way to migrate your Outlook mail to Entourage. I actually went from Outlook to Mac Mail by using a small program I paid $5 for that does the export for you very quickly and automatically. There is also great free alternative in NeoOffice (based on OpenOffice)
Hmm... so much more to say, but I'll stop there.