How to quickly and easily get rid of iOS 5 banner notifications -- the little roll-downs you get in-app and on the home screen -- seems to be a hot topic for our tipsters this week, and luckily you can do it in a couple of different ways.
In both cases you need to be really careful you touch and keep your finger down, otherwise it will be interpreted as a tap and you'll be whooshed away to another app, likely the exact the opposite of what you wanted.
Either way, it does nothing to fix the central problems of banners -- they roll down over content instead of pushing the content down, and they come in surprisingly enough that you can be about to tap a top-bar control only to hit a new notification instead.
Hopefully some sort of visual cue will be added, and the page content slid down, in a future update.
Thanks: @mpanzarino for figuring out the reliability issue with the swipe.