Relevant threads from the past:
http://bitcointalk.org/index.php?topic=227.0
http://bitcointalk.org/index.php?topic=1494.0
I think a fully licensed online bitcoin exchange to/from US dollars via online credit card transactions (or another really quick, convenient mechanism) is critically needed.
Is it worth attempting: I've been very tempted! Unfortunately, to do it right and jump through all the legal hoops would require at least posting a $50,000 bond and probably thousands, possibly tens-of-thousands of dollars to hire lawyers to get all the paperwork in order.
And then I'd have to figure out how to accept credit card payments for bitcoins in a way that didn't open me up to massive fraud (maybe secondary approval via a phone call or text message). And convince a merchant account provider that I'd solved that problem and that I was trustworthy (which probably means another infusion of tens of thousands of dollars to cover potential fraud).
I think it is a great opportunity for somebody (or some company) who has had prior experience in the currency exchange business. The business model is clear and proven, and being the first fully licensed bitcoin exchange would have huge potential benefits if Bitcoin turns out to be a really successful.