I've been using Gravity forms on all kinds of WP sites for almost 2 years now. Many of my WordPress sites are multisite installs and one in particular is a large network with 82 sites on it.
This one network contains all related sites (artist-painters) and the issue I've been running into is that, visitors that are already registered or subscribed to any of the sites on the network cannot "register" to any other as their email/username already exists on the network when they try. Yet it would make sense to let then register to any site they want on this network.
When we have users that want to register to more than one site they have to send in a request and an admin has to go in and add the existing user to the new site.
Couldn't the User Registration addon provide that optional functionality? The addon would have an option to allow multiple registration on the network (with maybe the ability to exclude certain sites) and, when a user would try to register to a new site on the network, the addon would simply "add" the user to the new site giving it a settable role (mostly, subscriber) just as admins can from the WP backend instead of just spitting out the duplicate/existing username/email error message. This is something I'd hope would make it in the addon sooner as I think I brought it up before (a long time ago) and, if i remember, the use case made sense to you guys.
On some networks it makes sense to isolate sites from one another but, in this case (and others certainly have the same requirement), we'd actually need users to be able to register to any number of sites they want on the network so having that option would make the addon a lot more useful for many people I'm sure.