It does look very similar. They also use some identical terms - Command Palette for example. Honestly, this can only be good for us.
1. Atom is so good that we can switch to it, and keep all the Sublime goodness and get even more (Atom will be open source, most of it that is)
2. Atom will force Jon to invest more into Sublime and do something like: speed up develop / builds, lower price, actually offer support / bug fixes etc.
3. Atom will force Jon to open source (parts of) ST to accomplish speedier development.
More competition is only a good thing. Sublime currently has the ecosystem advantage, but Atom will catch up with that quickly. Sublime also has a speed advantage, and this could be its selling point for a longer time.