I predict that Adobe Flash usefulness will start to slowly decline as soon as Mozilla Firefox 4 gets released.
I really hope that it wont be as slow as IE6’s death. If we are lucky, by 2015 we wont even remember what Flash was! Here‘s an article talking about the current release schedule. They’re aiming for an October RC1 launch. Final release should be in time for Christmas.
Update: Here‘s another article that explain new features of HTML 5 standard (a big feature of Firefox 4) and as a side effect, explains my claim that Flash will become obsolete.