I tried Cimy User Extra Fields, but it didn't seem to affect the registration page which I think is because of the Membership plugin. I could be wrong, or I may not have configured that plugin right either, however. It seemed to me like the registration page didn't change though because it is specific to the Membership for my group Subscribers - so I will be happy if there is a way to adjust it for the client who would like to collect more information at the signup stage and have it stored in the database.
Whenever possible, I would like to stick with your plugins also, so it will be great to know which way WPMU suggests for adding/removing signup fields.
Just for reference: