Phone geek: Unfortunately, the problem isn't with your iPad, it's with your Documents2Go app. I don't think it's been updated to play well with iOS 5. I don't have a solution for you, because I, too, had a pretty bad experience just now in trying to use that app to view a .xlsx file I had in Dropbox. As in, it didnt work very well and was just as bad as in your video.
Unfortunately, all I can recommend is trying another app to view Excel files (QuickOffice has good reviews ... thought I've not tried it) or waiting until Docs2Go gets updated. Not a good answer, I know - but that's all I got. Sorry. Maybe someone else can chime in with a good app they have that views Excel files well...
Oh, and for putting in the password while at the store? That's an Apple security thing, even for free apps. The only way around it, if it can be called a workaround, is to do downloads within a 15 minute timeframe, cause that's how long your password session lasts.
Gee, aren't I the bundle of good and helpful news. Unfortunately, I'm not. Sorry, again.
Marilyn