It does solve the Byzantium generals problem rather neatly, which is good. But I doubt that is why it is used. It is used partly because it suddenly became free money for a lucky subset of people who found you could exchange something you got for free for something valuable (drugs sex etc) - and those were at such high rates that the people receiving the bitcoins were also basically being given free money (when one read the official exchange rates)
This managed to fuel an interesting cycle. I would be interested in seeing if bitcoins exchange slips have affected it's purchasing power at exactly the same ratio or if it is being used as a barter not a currency (in these dark corners of the drug dealing world)
I would also suggest that (afaik) real drug dealers who do real big deals work on serious guarantees of trust. Things like knowing the person you are dealing with, and where their children go to school. So things like trustless currencies in these environments are not trustless - quite the opposite.