It's an in-order execution core with only 512KiB cache. It's designed for one thing and one thing only: running on very little power whilst still allowing people to run X86 apps to about the standard of your average Pentium III.

I swear I read a much better article about Atom, with better benchmarks and comparisons, at THG, a couple of days ago, but I can't find it anymore: it looks like they pulled it out.

by the way: Atom sucked quite a lot in that review, too