[exelius]

The rule of thumb that most VCs seem to follow is that within 7 years, 10% of your investments will be successful, 30% will become self-sustaining but never really go anywhere (think acquihires or small acquisitions) and 60% will either fail outright or barely survive. But keep in mind that this is among companies that actually made it to VC; success rates for angel funded companies are much lower.