Depends on what d3 is for you really. If you're dedicated hardcore gamer, then you might feel like you need to use RMAH to buy better gear. I don't really care. Never bought anything (well, I got one BB fury for buying a beer for my mate but that seemed fair hehe), sold some items (maybe 300€ in total) in d2, so I guess I'll use rmah the same way - sell something occasionally, never buy anything. What bugs me most is that 1.0.3 isn't here yet. Farming for my own gear makes my monk kinda stuck in a2, but that's another story.