You may have noticed in the right column of this site under External Links that my bookmarks are now with Ma.gnolia. I switched from del.icio.us two days ago, after a recent switch from Furl, for reasons that I explained last December.
I saw Ma.gnolia and instantly liked it. The interface is pleasing; there is a cached copy of your page (which Furl had but del.icio.us lacked) ; and the RSS feed is exceptionally nice, with a colour thumbnail and the comments included in the feed. Transferring my data was easy and Ma.gnolia even provides you with the direct link to your del.icio.us OPML file. All 600+ of my bookmarks were uploaded and put into Ma.gnolia, which seems to be much more social and human.
Update: I have switched back to del.icio.us as I had some export and OpenID authentification difficulties with Ma.gnolia.