I've been working on this for the past 3 months or so full time. Rails 3 + MongoDB. We're having trouble getting users to understand what a 'bookmarklet' is, so I'm having to create browser extensions (God help me when I get to IE).
It's marketed more towards women and the products they buy (they shop way more than men), but it can be used to save and compare just about anything that has a web page. I would love to know your first impressions or how to make it better/easier.