Creating a new currency is a chicken/egg problem, like many of the dilemmas that are a part of an emerging standard or technology. Many different things have been used as currencies throughout the years:
Shells, Stones, Grain, then Coins and Bills.
Good Currencies have these qualities:
--Scarcity
--Uniformity
--Durability
--Inability to Counterfeit
--Ability to easily verify as real
--Ability to easily (and inexpensively) transfer
--Multiple denominations / Easy divisibility

Bitcoin works 'cos it meets or exceeds these qualities, particularly for on-line transactions, as compared to cash. Bitcoins will take on value as people find them to be a valuable way of exchanging value. Adoption will go slowly, but exchangers are popping up all over the place.

Bitcoin's reliability and trust comes from the fact that it is a peer to peer network, a cloud. If Bitcoin was a hierarchical, corporate entity, then yes, I too would be concerned about a website for exchanging it being Slashdotted into non-functionality. But because it is a distributed network of peers, I trust that there will always be other peers to work with and interested in exchanging. Yes, if the whole internet went away, Bitcoin would have a problem, but so would most payment systems we rely on these days, and we'd have bigger problems to worry about than just the stability of the bitcoin medium.