iPad Applications definitely are. In the non-gaming world, Plangrid, drchrono, and Paper by Fiftythree have all been really successful, and that's just off the top of my head.
I'm applying to the summer batch, and I just noticed my company may fit into an RFS. Anybody have experience applying with RFS? Would it be better to just apply without it, and let YC make the connection?
For example, are "Things Built on Twitter"[2] and "iPad Applications"[3] still a valid way to build a $XX billion company in today's world?
[1] http://ycombinator.com/rfs.html
[2] http://ycombinator.com/rfs3.html
[3] http://ycombinator.com/rfs6.html