As for preference shares, most VCs try to get that. They can be negotiated away by the company management sometimes. If they remain, they come into play in situations where the company isn't successful - where the shares are sold at a lower value than they were bought for. The preference gives the VCs to get their money out first, and leave the scraps for the others. Usually the others includes the founders who are similarly shafted - but then again they evidently didn't build the value of their company very successfully and they signed the deals.