At my friendly local framebuilder, Ti bikes are a $900 premium vs. Tig welded steel; about a $700 premium vs. lugged steel.

Other than the price I can't think of any downside.

The worst insult I ever saw about titanium bikes came from Mr. Retrogrouch himself, Grant Petersen. He was once quoted as objecting to ti bikes because they are "ghostly" in appearance (apparently unaware that Ti can be painted, just like steel). If that's the most that he can come up with, I figure it's not too bad.