Obviously, mainstays like search engines and rss readers would be assumed everyone uses regularly.
Good mashups are worth stating.
Social proof, especially here, is valuable.
Which has been helpful in collaborative grocery list creation among other things.
-- I also use a slinkset site aggregating many feeds of new website releases.
I am proud of it, traffic hasn't really climbed even after spikes from being linked elsewhere, like on a TC comment, so I'm thinking it's more of a very niche site.
It avg's only about 50 uniques a day.
I'm generally averse to wasting people's time, I'm also somewhat detached to the worldly success of the site as I'm happy using it myself. Also, I think as a twitter client, there might only be 2 others that use it regularly for that purpose.
Side note: for a while I started collecting information about what people were doing on the site using ajax posts to the server as it's all client-side, and I found a regular Chinese user who'd possibly setup a bogus twitter account of a fictional gay character linking to products for all his followers.
It's going to need about 3 times more traffic to start getting feedback and PR momentum. I think the site will only stick with a small portion of people that visit it. So it'd need to be hyped a lot, which is not my thing if it ends up wasting people's time in the process.