Delicous has managed to destroy itself in a single day. That's impressive by any standards, but I really think that they've done it. Users are complaining that they can't log in, and then when they do they're finding missing tags, no RSS feeds, the search function has been wrecked, tag bundles have disappeared, and that's just for starters. What do we get in return? Something called 'stacks' which are not interesting, novel or indeed new. At all. Plenty of other people have been doing them for ages.
The Delicious page over at Facebook is where most people are venting their spleen, and I've yet to see one complimentary comment. I really didn't think it would be possible to screw a service up that badly so quickly, but the new owners have managed it with stunning success. If you're looking for an alternative, and didn't jump ship last year, my blog post back then provides 28 alternatives to Delicious - I'll be going thru them to make sure that they still all work, but it's there in the meantime. I've had diigo as a backup for the last year, and I moved across today, lock stock and barrel. I suggest that you look around yourself!