First off, simply cause it's probably easier to implement, is to have items you buy on buyout in the AH go directly into your inventory if you have space instead of having to go check your mail to get it. It's just inconvenient and a bit annoying. The ideas posted here are good too.

Second, I've noticed that rifts spawn in set locations...this kind of lames the concept a bit and dulls the 'fantasy realism'. They should spawn in random locations. Also, I would like to second the other rift concept posted here.