It's overvalued: Firstly if you buy the site that doesn't mean that you get the audience and the good will that the site/brand has now: The brand with the value is 37signals not Sortfolio. Secondly running it "as is" won't grow the site, you'll need to invest a great deal of money in adding features and growing the audience (so "tons of untapped potential" actually costs you money). And lastly if you think that it's that great of an idea you could most likely build it for far less than $480k (and contact the current soon to be alienated user base).