The biggest problem with Bitcoin is that if these people decide not to give you your coins back, let alone your interest... there is absolutely nothing that could be done about it. It's all done instantly now... So the second a site doesn't give your money back its game over. They take everything or nothing. I'm saying it's generally binary, the moment an investor can't take his money out he tells the world on the Bitcoin talk forum and the site either needs to pay or it will have to shut down as a scam.