The OpenID logins don't seem to work properly? I clicked the G logo to use my google account, but I ended up being asked to create a username and password anyway. Also (at least in Chrome) the links don't have underlines or change when you hover over them in any way, so it's not clear they're links.
Great idea though. I'd like to register but having to update every week seems a bit much. I am usually around my home city, if somebody wants to buy coins from me, that is all the info needed.
We require a username and some remote authorization providers don't give one. We just deployed a change so that if a username is available it will show up in the dialogue. When using a remote authorization the password is always optional.
We also made links last for 6 weeks now. This is just for the beta. We'd love to get input as to the best length of time. On the one hand you don't want to have to update it too often, on the other we don't what a bunch of pins on the map for people who've moved on, or aren't using the service anymore.
We'll look into making the links a little more clear.
Thanks for your input!