As far as needing to be online to play single player, I'm pretty sure that offline single player is on their short list of "coming pretty soon" features. I know that the devs aren't intending to have strict DRM or anything.
I have a couple of thoughts after several games about a minor UI tweak for auctions, similar in spirit to preventing bidding against yourself (which has already been discussed). A minor issue I have experienced is inputting a bid slightly higher than I intended by clicking slightly after another player's bid goes through. I have 2 suggestions to help with this, one of which is something you likely already do. First, I'd like to see a client-side delay (half a se