What amount of RAM are you targeting, and will you warn users of devices with less than optimal RAM that you haven't tested on their devices?

This is an interesting question, but I doubt it really is anything you need to be concerned about unless you are creating a really, really heavy applications or game. The minimum RAM requirement AFAIK is 256MB for MeeGo and that's pretty plenty.

Not to mention the fact that C++/Qt is less memory-hungry than interpreted or VM-like languages. The difference isn't big by any means, but it still does exist.