Most successful startups launched during tech conferences?
pedalpete: I think all you need to do is go back to look at the conferences in the past and see who launched. 
Here's TC50 from 2007
http://www.techcrunch50.com/2007/
You'll recognize a few names who are doing very well now, 
However compare that to last year
http://www.techcrunch50.com/2008/
and I don't recognize a single company their as reaching a critical mass in the last year.