There are a few dual core Atom CPUs that have hyper-threading and are good enough for anything but gaming. I wouldn't touch a single core Atom if you can help it, though. And if you're doing any kind of heavy processing, well you know Atom is not going to be for you.
Some site, maybe Tom's, did a comparison about a year or so ago and concluded that the modern Atom CPUs have about as much processing power as a Pentium 4 had, but of course they are much more efficient, as well.