Was in the batch with these guys - kickass product. I love when I run around the web and I see it in use by a random group of folks I didn't expect would know about it (eg Fred Wilson from earlier this week : http://www.avc.com/a_vc/2012/11/mba-mondays-the-revenue-mode...)
Meteor (the company) uses Hackpad extensively and I don't know what we'd do without it. We do almost of our systems and API design in collaborative Hackpad documents.
Do you have to download/save documents every time you want to view an HTML page or run a new copy of a python script? If they've have a way of saving a copy locally while working on it online then I'm in.