OK, I don't know how many people here actually have a mac, but I do have one so I speak from experience ;P
Personally, I think windows is better. It's much easier to find software for, and typically seems to be faster. I know, my mac's rather slow, but I mean I even compare a PIII 733MHz(windows XP) to the Mac Mini, and the PIII does similar stuff much faster than the Mac.
I've had lots of problems with OSX. I hear since OS10, they lost the "true" mac feel. I know it's quite difference since my last experience with MacOS 8... Besides the change, I've had many little problems with my programs. Firefox, my chat client, Premiere, Photoshop... They all give me errors almost every time I use them.
Eh, I just don't know... I can't find much good to say about my mac. I really like it's size and how it's next to slient, but...eh, that's about it.
