If you're getting praise for the UI, go for it. I think my biggest issue is the relatively narrow nature of the design. The cards, the columns, etc. Example: http://cl.ly/1i01452a3l0V1X3K3N1f -- line breaks like that are difficult on the eyeballs.
Little things, like using color-coded labels for organization sound good on paper, but are very tedious in practice. Lots of calendars use this with good intentions, but you'll find yourself asking, "is that a grey, or taupe task?"
Walking the user through the on-boarding process would help immensely in describing the product. Right now, there's a bit of information overload with everything being visible on the screen. It'd be neat to see an approach where you're presented with nothing, and are told to "create a list. Great! Now add yourself to this list. Wonderful! Lists are used for X, Y, Z"
I do apologize for being so gruff in my original comment. If you're getting great feedback on Trello, there's obviously something there. Good luck with it!