We got a couple of new servers at Solfo recently which showed me one of the reasons virtualization is so popular now: Servers are too fast!
The "standard issue" CPU is now a quad-2.5GHz CPU, so in each server we have 20 GHZ CPU and 32GB ram (at less than $50 per gigabyte it's too cheap to not just fill it up and be done upgrading). Just a few years ago the CPUs we were getting were "only" dual 2GHz, for ~8GHz CPU per box. That's a big increase!
In each "tier" of the application (app servers, db servers, search servers) our main reason for having more than one or two servers is redundancy / high availability - never lack of CPU and rarely because we need more memory.
Here's from one of our webservers (virtualized with Xen with 6 of the 8 CPUs on the "real" hardware).
The big exception is the MySQL servers where we get constrained by I/O so we need a single chassis with lots of disks (the $$ version would be to get external enclosures or SAN boxes with disks) and of course in the MySQL servers we can easily use all 32GB ram.
Anyway, the conclusion: Please give us cheaper, lower power CPUs. More memory, sure - we'll figure out to use it. More disk I/O: yes, please! More more more! Faster CPUs makes sense at scale, of course, but for a smaller website with just a handful of million visitors a month we just can't make a dent in the available CPU. Maybe if we used Ruby instead of Perl. ;-) (just kidding).
(I realize that AMD and Intel makes plenty "slow" CPUs, but they don't come in server boxes with fast I/O and all that).