We started using Quad Cores with all our newer servers in November and love what it has done for us. We're seeing more power avaialble for the users but we didn't increase the number of accounts on the servers (so that plays a big part).

Pentium and Celeron will still be offered as many people want a cheap server to get into the field. Personally, I'd not use a Celeron for anything other than a DNS server or a testing machine.

I don't buy anything now unless it's QuadCore. Pricing is almost the same between a QuadCore and a DualCore with the extra memory needed to compete on the same level.