I'm typing this on a G5 powermac from http://www.scrumpymacs.co.uk – I think it's from mid 2006, running 10.4.11. with 1Gb ram.
Next to it on the desk is 2 year old custom PC (won't bore you with specs) running Windows 7, with 4Gb ram.
Old Mac is twice as fast booting from cold, and runs CS3 much faster.
At home I've got a Macbook refurb, about 4 months old – awesome – £579 direct from Apple.
Are they worth it? Yes, because my wife has no idea how to work a Mac, so leaves it well alone.