Now that they're shutting it down, I would love to hear your thoughts as founder on why delicious didn't live up to its potential.
having been part of one particular exit I know all too well that startup founders and ex-employees have deep emotional connection to their former company, no matter how much they got for it.
Depends on who you are. To the investors, that would be a failure. To the people that find it useful, it wouldn't be a failure until it disappeared or otherwise ceased to be of use.