I guess that about 20% of the 7,000+ initiatives that I've indexed between 2006 and 2008 (in my EVERYTHING 2.0 blog) have disappeared from our screens. A considerable number were just fun projects, without any business perspective. The better ones got acquired - I guess 70, or so. A few of the weaker-but-still-interesting-enough found partners to merge with. But most members of the 2.0 Death Pool just perished.
Many of them did it graciously, diligently informing their members, sometimes even giving them time to remove their data. But, still, quite a number just stopped their activities - in mid air, so to speak.
During the past 12 months I've sometimes captured the messages that I got (over email) or found (on a dead web page).
This collage draws the whole picture (especially when you have good eyes).