Right now, my priority with Atomo is consistency in the design and simplicity in the implementation. It's acting as an incubator for a ton of interesting language features at the moment (both for myself and for Slate), so I haven't made optimization a priority yet as major parts of it are constantly changing. For example, the version on Hackage has a traditional exception system, while the latest darcs changes have replaced that entirely with a condition/restart system written in Atomo.

I'd call it "fast enough," but it's no speed demon. It's pretty early on; I just started planning Atomo's design this June. There's almost certainly some low-hanging fruit when it comes to optimization, and it is something I've been keeping a close eye on for a while now. It's only been getting faster, and in my testing of GHC 7 I saw pretty substantial performance boosts for free. And that's the nice thing. It's built on a fantastic platform, which you can drop into very easily whenever you want with a nice DSL.

Glad you like it, though. I completely understand the caution when it comes to performance of such a high-level language.