BGG's Rustan Håkansson has been using the app in its most recent incarnation at Spiel and notes that it's working well here. The most important thing to note is that you need to do a full "Load from BGG" and let the process work all the way through, then after this you can load your wishlist to be able to show only the games you have marked here on BGG from the Spiel 2012 Preview.
You don't need to go through the "upload other booth info" process as I added nearly all the missing booth information on Monday and Tuesday while in Köln. Working vacation! I also added a number of other games to the Preview during this time. Still haven't got everything on the Preview, but I'll report on surprises while reporting from the convention. For now, though, it's time to head to the Zoch Verlag booth in order to check out its newest releases in person. Yes, I'm actually going to *gasp* play a game. Who would have thought that's possible?