I've been using del.icio.us to provide categories, descriptions, and various metadata for Blogger-based shopping cart weblogs [1]. It has done a wonderful job of supplementing the simple data repository at Blogger with gobs [2] and gobs [3] of metadata for the websites I'm managing for others.

[1] http://www.crystalflame.net/2004/09/one_hour_from_n.html

[2] http://del.icio.us/coronahats

[3] http://del.icio.us/coastalglass