In my experience, a MAC processor is generally equivalent to a PC processor 80-100% faster. So a 1.8ghz Mac might feel like a 3ghz+ PC. I do a lot of computer rendering at work and at home, and my powerbook (I think its a 1.8ghz) beats the pants off the 3.4ghz PC I use at work.
I've always had a PC wherever I work, and have had a Mac for home and when I was in school. Every single PC I ever used always got plagued with errors, malfunctions, viruses, spyware, and stuff I just could never figure out and had to get IT to fix. My Macs have never had any of these problems.
The only issue I have with Macs is the lack of software, but that will change once I can afford an Intel Mac.