I really like the delicious plugin for firefox and have been recommending it to people for a while now.
Recently though using the plugin with firefox 3 on both Windows and Linux (Ubuntu) has been a real pain. “Favorite Tags” and “Tag Bundles” have been disappearing and losing their settings. This has been going on for a few weeks now and the developers have been working hard on resolving the problem, which turned out to be a corruption in one of the settings files.
They have released a beta fix for this problem, which you currently have to sign up to a Yahoo group to download. Details of the problem and how to obtain the patch can be found here.
Hopefully they will release a mainstream version of this patch soon!