Well, this one is, by far one with a very clean, no-nonsense UI. It means business. Being developed by my friend Jeethu, it is mainly an experiment to see what happens when you mix social bookmarking like del.icio.us with social sites like reddit. Though it began with that in mind, Jeethu has not stopped adding usefull features http://tagz.in/help/ http://tagz.in/tagz/whatsnew/ . And knowing a bit of his plans, I can assure that several are on their way.
Oh! before I forget.. he also has a reddit page , uservoice page, and obviously a blog of his own. He likes coding in python, and as on the about page, uses django and other python stuff.
It is clearly evident from my monopolization of the website and the uservoice pages that I am really liking it. :-)