These are not the success stories of Sparrow, but 3 that I recall that when purchased went dark in some form, to (possibly) re-emerge less than their former selves.

http://etherpad.com/ http://arstechnica.com/business/2008/01/jaiku-users-flee-to-... http://techcrunch.com/2008/02/27/it-took-16-months-but-googl...

Its not to say that this acquisition is not a great thing for the Sparrow team, or that Gmail may someday improve (UI wise), but it is an unfortunate trend for users when a great small / niche product is absorbed and obliterated.