Dual Core Goodness
I've been working on a dual-core PC for the first time over the past week and I have to say that I really...really like it. The user experience is much more fluid than it is on a single core machine...even with a relatively low end dual core CPU. I can build a large VS.NET project (build takes ~2 minutes) and the machine is totally responsive while the build is taking place. In genreal, the windows shell is never unresponsive on the machine which is a very nice change of pace.
Memory helps also...the machine has 2 gigs of RAM which is the sweet spot for a development machine at this point.
So, especially for developers, I would strongly reccomend a dual-core CPU even at the expense of less overall processing power (e.g. get a $300 dual-core CPU over a $300 single-core even if the single-core has higher benchmark scores). Trust me - you will be happier.
Oh yea, go for AMD CPUs whenver you get the change. Not only do you get more processing power for your dollar, you are also supporting a company that supports one of my passions.