I own a MacBook Pro (not upgraded to the new Mac OS - Leopard - yet) and a Vista PC, and I also have a Vista Notebook at work.
My Vista PC never had any trouble I can remember.
I remember that my MacBook Pro had some trouble with some videos I once tried to play with FrontRow, but since I switched to the VLC Media Player, I haven't had any problems. (VLC is definitely my choice both on PC and Mac)
My Vista Notebook is "Designed for Windows XP" ad "Windows Vista Capable", which isn't exactly optimal for Vista, but it works fine (it's a bit slow for software development purposes, though), but I'd like better graphics driver and coming from sleep mode doesn't work all the time. But I also attribute this to the PCs.
I am not sure I would choose a Mac again. As a secondary machine it works, and I am doing a lot of my role-playing stuff on it, and I am watching movies on it (connecting it via DVI to my wide-screen LCD.)
But if I look at the games I am interested in (and that aren't limited to video consoles), the PC is a must. I think OpenOffice works a little better on my PC then NeoOffice on my Mac, but I can't lie on the sofa with my PC.

I also usually surf the Internets more with my PC than my Mac.
If you go Apple, you will undergo a small learning phase with the slightly different keyboard layout and differences between Windows and Mac GUIs)
EDIT: I love the Apples "Viewer" - way faster then Adobe Acrobat Reader for viewing PDFs. It eventually lead to me getting FoxIt for my PC, since I couldn't stand the slow loading times for Adobes Reader any longer.