I can't believe no one mentioned the most objective advantage of bitcoin: I can send money around the world without paying anything.

It may not be that useful to the average consumer, but it is the first currency that allows this. For example, I am an european and I really like dealextreme.com because they offer free shipping and they sell cheap stuff. I would really like to pay them with bitcoins because I lose a lot of money with the EUR/USD conversion.

Also, bitcoin is not anonymous by design. It allows for a certain degree of privacy and it can be sort of anonymous, but you must use other tools for that. I agree with most of what faustianover said. Bitcoin does not have one simple great advantage for consumers. It is technologically rather interesting and it offers some interesting features that some people want. However most consumers simply don't find these attractive enough to justify the change. At least right now.