"Contact" form immediately responds with "You cannot send more than 3 messages per hour" so I'm trying a forum post instead. Maybe other people will have some good ideas to contribute, anyway.
New site has a nice clean design and loads quickly. Nice job and kudos to the designers and implementers. The ability to upload small files is an especially nice touch and it should enable people to share articles, charts and documents easily. I've launched a couple websites or major features in my time and I know it is tough to make that "feature freeze" call, stop adding new features, fix bugs, and just ship the damn thing.
One thing that is always useful is to have a feedback mechanism about the site/feature itself so that people can get help ("how do I...?") or report usability problems, browser incompatibilities, or bugs. Maybe a "Help" or "Troubleshooting" forum?
This part is mostly for the developers. I had one problem with the account creation flow, and a few suggestions:
Bug report: on my first try it didn't accept my CAPTCHA and sent me back to retry, but it deleted the password I had entered, so when I entered the CAPTCHA again, it failed for no password. On the next page there was no CAPTCHA form, so I re-entered the password, it failed again for no CAPTCHA present. So I think there is a bug with the presentation logic not displaying the CAPTCHA on some conditions.
Suggestion: Time zone selection was pretty awkward with the huge list of cities, and fairly major cities missing (Seattle?).
Suggestion: Make it more obvious what the site is doing with location information. A lot of people keep... stuff... at their house. Wasn't sure if this was going to be public or private info. I deleted it. But setting the default time zone based on the location, if the user provides it, should be doable.
Suggestion: Increase visibility of OpenID choices. Based on the video I thought only Facebook was implemented. I didn't notice Twitter until I had completed the account creation pipeline.