Re: Which CPU?
The AMD's are good for general purpose computing, they're not the fastest out there, but for most users, it's not noticeable. they DO excel at things like h.264 video encodes, and for low cost gaming when paired with a high quality / high performance video card.
Intel's i5 and i7's are the fastest out right now in terms of overall performance. You can get about 80% of the Intel performance in most tasks by going with AMD (currently) and that number can be up as high as 100% or more in some tasks.
For reference, most PCs that use Intel and AMD processors paired with a high end GPU will often post very similar or the same benchmarks at higher resolutions.
I'm not trying to ding AMD (look at my avatar and my PCs in my sig) by any means, but I know their weaknesses. The Intel chips out currently are based on new tech, while the Athlon/Phenom lines are based on a 2007 design that AMD hasn't re-engineered since (Bulldozer should change that next month hopefully)