[mmcclure]

tl;dr At this point: not much. That might change soon, though.

When I switched laptops recently, I made the conscious decision to only install Atom to see how things went...so far so good, although at times it does bog down pretty noticeably, and this is by far my biggest complaint. There's also no alt-drag support (to create a straight line of cursors like Sublime), but that's a fairly small gripe.

I loved the plugin ecosystem for Sublime, and in the short time Atom's been around, the ecosystem has already exploded. Lots of awesome themes and plugins are already available, with more coming every day. The low barrier to entry (most things can be done with JS / CSS) probably has a lot to do with that.