quad core is nice for power users. my dad is still fine on his P4 2.8. He plays Flight Sim all day every day.
Me...I get pissed at my duo for lagging out while im playing WoW, Watching A movie, Letting another movie rip and occasionally browsing the internet while im playing.
It depends on your usage habits.
EDIT*
I have 4GBs in my workstation both at work and at home...and i usually utilize most of the ram and CPU at least once a day.
(Apache, MySQL, Ruby/Rails, Tomcat, Firefox, Email (thats half the memory right there), couple open office windows open).
I just realized, for a sys admin, i kinda have a developer style computer setup.