Social networking site Facebook has raised more than $150 million to stop its employees cleaning up if the site starts making a lot of dosh.

Hundreds of the Palo Alto, Calif.'s employees have now worked at the outfit for more than two years but are unable to cash in the shares. While selling them back to Facebook will net them a nice windfall it also prevents them from seriously cleaning up if the site does a Google.

At the moment they will be allowed to flog 20 per cent of their shares back to Facebook for about $10 a go. Facebook is not going to become a public company until the economy spruces up a bit. 

When it does, those shares that are still in employee hands will cost a bomb. So it makes sense that Facebook can buy them now for $10 and clean up in a couple of years time when the outfit goes public.