I'm currently using WordPress 3.2.1, BuddyPress 1.5.1, with Gravity Forms 1.5.3 and User Registration Add-On 1.2.9.
I noticed recently that there was an update for these (GF 1.6 and URAO 1.2.11) and without thinking about it updated them. This caused user-registration to fail. The form still loads, you can click through everything, it'll come up with the message telling you that it registered you, wait for an email... but it doesn't actually do any of that. No email is sent, no user is registered.
I have reverted back to GF 1.5.3 and URAO 1.2.9, which works fine. What changed between these versions to cause this behavior?