My biggest issue with Trello has been that if you have two windows open, the changes don't sync between them. Pivotal tracker does this extremely well making it a team collaboration tool
If you have two windows open in Trello, the changes do sync between them. If you're not seeing that it's a bug, but that particular feature has been pretty solid since day one.
I just tried it again and it does sync. Weird because many times it has not happen before. May be flaky internet?
We had a connection bug 3 weeks ago that could have caused changes to not sync. If you still have any windows that are not syncing, please email support@trello.com as soon as you can.
If you have two windows open, the changes DO sync between them. That's actually the whole point of Trello.