The community supported version of MeeGo (the only one the N900 will get) will very likely not have any of the Nokia apps on it. No Maps, no Messaging, etc.

I would either buy a dedicated unit (defeats the purpose of having such a smart device), or keep an eye on nitdroid. As bunason said, it works very well. Far less frustrating than using Ovi Maps. Frankly, I'm considering removing Maps and its data, and just boot over to nitdroid for my navigation needs.