Well yeah!!
Stuff like "select and repair non-manifold edges/surfaces"... "remove/repair self-intersecting faces"... "align all faces for correct printing"... "merge multiple 3D objects".
They're just a few that I can think of that'd be mighty handy!!
If you can make your app that little more capable even than 'Netfabb cloud services', I'd reckon there'd be quite a few reprap operators who'd switch or at the very least leverage both to sort out their printing issues - especially those caused by the problems my suggestions above would help eliminate!
And in case other's don't say it... Nice work; and thanks for your generosity and efforts as well as the consideration!