Angel investors often provide a start-up's very first infusion of funding. In uncertain economic times like these, angels tend to guard their cash carefully: They tend to shrink how much they'll put into a company, and look to diversify their investment strategy—offering smaller amounts to more companies, accoridng to Jeffrey Sohl at the Center for Venture Research.

Average size of angel investments:

In 2005: $523,232

In 2010: $324,717

Number of angel investments:

In 2005: 41,500

In 2010: 61,900