In recent days a number of modestly successful online social and productivity services have been scheduled for decommisioning. Pownce is being turned off as that team moves to Six Apart, and I Want Sandy is going away as Rael moves to Twitter. You will see more systems get acquired and shut down with graceful exits, and some exits will not be so graceful.
There seem to be multiple common reasons why upstart systems get wiped out in times of economic crisis. If your traffic is not growing and you aren't attracting legions of superstar users, it starts to look expensive to bet against a bigger rival. Even if you do manage to pull off steady growth in usage the test may be scaling up your infrastructure to keep pace with demand.
If the dot com crash is any predictor of future consolidation, look for the survival of systems that address some specific real need of some narrow niche and that don't have to grow to planetary size to be profitable. Display advertising rates continue to fall, making it more and more attractive for people to run house ads instead selling merchandise or services directly to whatever audience they can sustain. If what you are using does more than just scratch some coder's itch you have a better chance.
Web 2.0 is over. Back up your important data now, or decide which parts of it you are willing to discard.