Several major +1s: 1) Use of Google login, with ability to set a password to log in without that. I LOVE this, and it fits with what Joel (and Jeff Atwood) have been proselytizing for a while about the use of OpenID.

2) Awesome, responsive UI.

Also a few -1s: 1) No indication about pricing plans. Is this going to cost money one day? EDIT: I see now that you mention in the blog post that it’s free. And the site says "Creating an account is free and easy", but you know how often sites say that but mean "creating an account is easy, but to use our software in any meaningful way you’ll have to pay."

2) I had a problem when I created a new board. The UI took a while to respond, during which time I got confused, created another new board with the same name, and ended up with two new boards with the same name.

Suggestion: The menu that opens when you click the arrow in the corner of a card should open with right-click as well. This is how assembla’s card board works, and I like it that way.

Suggestion: Labels should take one click, rather than two. On the menu row for labels just have six colored squares to click on. Maybe that won’t work so well for smartphone users, but for a desktop, I’d rather save the click.