I 'switched' almost a year ago and I'd never look back.
(Having attempted to configure my little brother's Win2k Sony VAIO for a wireless connection over the weekend, I almost kissed my Powerbook for its simplicity on my return to base.)
An important thing to remember is that G5 towers are mainly used by graphics/music/moviemaking professionals as workstations, and their price premium reflects this.
I can wholeheartedly recommend a visit (2 hours!) to the new Apple Store on Regent Street....it's the absolutely stunning future of retail and an excellent opportunity to get acquainted with the Apple 'experience'.