I've in the past written some keys as to why start-ups fail on my own blog. I do like the idea of a big formal launch event, either at a conference, or awards event, however, this isn't always as easy as it seems, and typically can cost valuable dollars that Start-ups might not be willing to spend.
When I was at Crosswalk, we tried to re-launch the company at Super Computing '06, I think we ended up spending roughly $400.000 between booths, lanyard sponsorship, etc. We even won an award (or rather bought an award). In the end, it didn't help us gain any additional prospects.
Here is a link to one of the start-up write-ups I've done.