Late to the game here, but in addition to the others’ comments, I’ll add the following (as a Mac user for 20 years and a PC user for 10):

The mini is great ONLY if you want a small, attractive form factor. It is not as inexpensive as its base price would lead you to believe after you add the necessary RAM (512 MINIMAL, 1GB much better). You might also want to add a faster hard drive (it comes with a 4200rpm version… slows the system down significantly). To add these items, you need to open the machine, which is somewhat tricky (instructions and video can be found on the web). After adding them, along with a wireless card (if needed… should be added when purchased), the price will climb to $800-$900. All for a system that’s slow-ish (although, to be fair, it’s about the speed of my current personal system).

The Powerbooks might make more sense if you need portability. The iMac definitely makes more sense for power and value. Apple’s tying their system more tightly to the hardware these days, using the GPU to speed the interface, etc. The mini just doesn’t have the chops to give you a great experience, IMHO. If you’re only using it in a limited manner (web work, writing, e-mail, music, etc.) then it’s okay, but any significant Photoshop, video or animation work will leave you wanting more speed eventually.

But a Mac is definitely worth the investment. The system organization really has become more like Windows if you look beneath the GUI skin. After you see the similarities, it’s much easier to find your way around. Easier and better, I might add.

All the app questions seem to have been answered as well as possible. I’ll vouch for MYOB for books, although it’s not really a replacement for QuickBooks. It has a QuickBook import helper (as useful as these types of things normally are), but I have yet to find an accountant that takes MYOB files. My recommendation would be to either continue using your PC or use VirtualPC, which would probably be fast enough for Quickbooks (still irritatingly slow at most things).

SnapzPro is great (fantastic, even), but doesn’t automatically resize. It does do great movies, though.

A KVM works fine with a Mac and PC… at least the Belkin models do. Make sure you get one that uses USB and DVI (and audio is a help as well).

PC mice work fine. Absolutely. I’m not sure what the previous poster found objectionable, but I guess there might be a bit more variability in the right-click mode, due only to individual programs, not the OS. And there’s a program called USB overdrive that will allow you to reprogram any button on any USB device.

That brings us to individual utilities and freeware/shareware. I think there’s a healthy amount out there, and it’s usually much more polished and well-thought-out than on the PC side. Versiontracker.com is a great source. The good news is that grassroots development is on a huge upswing with OS X. It started with Next, Unix and Linux developers migrating over, but now is in full force. It reminds me of the early 90s, when small, clever apps were always cropping up.

Finally, you should know that it won’t be easy, quick or cheap to incorporate any of this stuff. And if you’re even mildly happy with your current setup, it probably won’t make sense. Unless you’re after a system that has the overall stability of Linux with the consumer apps of Windows (most of them, anyway). And is more flexible than either. And just does what a computer is supposed to do – turn on and get to work. I migrated to Windows 10 years ago and came back about 3 years ago (with OS X… I knew some Next developers). I still own and maintain more PCs (6) than Macs (2), but I only boot my PCs up when necessary (3D work and occasional financial software).