I've been in the Asana beta for a while & while it's a nice product, as far as I can tell, http://www.getflow.com/ is better in nearly every way. I just logged into Asana again today & it looks like they have started copying some elements from GetFlow, like the tabbed projects/tags/people bar on the left.
Anyone seriously use both tools & have an idea of their comparative strengths and weaknesses?