It's already a bigger economy than some small countries. That's a pretty decent size in my book. Add to that the fact that it's increasing in size exponentially at the moment and it's looking like it's going to be a pretty serious currency.
This is a big problem that does make it a toy currency. The slow exchange probably brings up the price. I expect, without much proof, that the USD:BTC ratio would be lower, at least short term, if you could exchange them easier.
$2b in circulation is pretty decent of course, but if you cannot convert those BTC to USD with ease then the valuation is flawed.
3 days is still a very long time compared to the 'real' currency exchanges.