Yesterday we did MineSweeper with almost no upfront design at all. We also had the biggest group I've been in for a long time. So we ended up being a little unfocused on the direction. A lot of minds pulling in different directions. It's hard to find the balance between guiding the group and letting the group make its own mistakes.
Since I'm still waiting for my windows phone 7 I have not tried the planning poker application (you need to be signed in to see it) that is available but from what I've seen it's good idea. Keeps people from using their phones for email and surfing during the planning poker session which something I've seen in the past.
Today was the second time I organized a dojo in my new team. We did the MineSweeper and it turned out interesting as usual. The highlights today was how the design got pushed in one direction by a typo in a test. The typo made us expose the internal representation of an mine field before the sweep which I don't see that often. Also the use of enums was definitely the result of having a specific person taking the keyboard at a specific time. Will be fun to see what we can do with the MineSweeper the next time.