Just don't wipe like 20 times. I lost track of most of my apps after tinkering with my phone for a few days...not too big of a problem. I had all the important ones retained in my history, but somehow a bunch just disappeared.
I had to do a factory reset to resolve an MMS problem. Lo and behold, after I rebooted my apps were still in the app drawer. I had to reconfigure my screens and reactivate some (Yelp, POP3 email, Facebook and Tripit come to mind) but otherwise, it wasn't a big deal.
This is a good question, and something I'm interested in. On a BlackBerry, each phone as a "PIN" that identifies it so you can (sometimes) easily transfer paid apps from one phone to the other. Is there such a thing with the Droid? Or is it tied to a Gmail account or something?