For UK readers this video by Ed Bowsher from MoneyWeek gives a quick overview of investing in startups and SMEs via crowdfunding. This is a good primer for anyone interested in investment crowdfunding.
Ed touches on reward based, debt based and equity crowdfunding. He admits he is not that interested in rewards (as he has enough T-shirts) he is quite keen on equity crowdfunding. Ed notes that investing in startups is very high risk and the chance are that you will purchase shares in the next Facebook are pretty slim but it is pretty exciting and there is opportunity to capture some significant returns. He quotes a report that was done in the UK that reviewed startups from 1998 to 2008 and if you, as an investor, had purchased equivalent shares on all 1080 startups your average annual return would have been 22%. Not too bad. Definitely worth a few minutes of your time.