After Delicious was unceremoniously kicked out of Yahoo!, it has become slower with every passing day. Looking for an alternative to maintain my bookmarks, I finally switched to Diigo. It is kind of a bloated service with lots of features among which the bookmarking is the most important one. The bookmarks have the same tag and privacy features as Delicious.
The good thing about Diigo is that I can export my bookmarks from Delicious as a HTML file and Diigo can import them all in. If you had a lot of bookmarks, Diigo will take a couple of hours to show your imported bookmarks after you hand it the bookmarks file.
I was using a Delicious bookmarklet to add bookmarks to it from my browser. Diigo has a similar bookmarklet which can be got here.
If you are not sure about letting go of Delicious, the best part is that you can allow Diigo to post every bookmark you add to both Diigo and to your Delicious account. You can setup this feature here.