We do. Its hard to list every framework/library in there, so they're not all mentioned. Look for a future technical blog post that goes into more detail on what we used.
Trello does use Socket.io. If your browser supports websockets it will use them, but it will transparently fall back to polling if necessary.
I user Chrome 14 and updates take over 5 secs to be synced across different tabs. Some kind of a bug or the backend app polls the db regularly to push new messages ?
We're scaling back a little to handle the usage spike from the initial launch, so some users will get polling even if their browsers support websockets. As the load stabilizes, we'll be switching them back on and you should see performance improve quite a bit.