Arg, going over the alternatives in this thread and on the web, I fear the actual loss of delicious is its useful dataset.
With so many competing products vying to take its place, it will probably be a while before a de facto bookmarking service comes along and gathers a userbase large enough to be useful and years beyond that for that userbase to build the data to a point that approaches what we had with delicious.
Maybe some sort of anonymized delicious data export would be possible?
Depending on what you use in delicious, pinboard.in may be a good replacement. It has all the things from delicious I used, none of the things I didn't, and a few other cool features (like saving notes directly, rather my my system of saving pastebins).
I absolutely _need_ a viable delicious alternative, too. xMarks looks like the closest bet, but their UI isn't intuitive and it's coated in ugly.