We all need great hosting optimized for scaling if our ideas get crazy popular. But until then, you need something that you don't need to worry about, so you can concentrate on building and testing your product.

We recently switched to PagodaBox, because I have no interest in handling sysadmin stuff at the moment, and I'm loving them (writing a blog post about it soon).

Cross the scaling bridge when you come to it. In the mean time, find something solid that just works for now.