Money is a thing with strong networking effect. That's why people doubt about bitcoin. Since USD is so widely accepted, why another kind of currency? Bitcoin will work out as it has something USD really does not have, such as buying drugs on Silk Road and send money to the other side of the earth without fees. However, as bitcoin is already there, any other alternative XXcoins won't work anymore.

Everyone make their own IOU just like everybody set up his own Bit Torrents, you're kidding, right? you share the files with yourself?