Phil,
Right now, after the initial Javascript click, all the communication is server side. We don't have any hooks that we could implement to get status right now, and depending on a lot of factors (mainly how many profile plugins are enabled), the percentage would be different on each site.
One thing we're looking into with the next release (v5.0) is reducing the amount of calls to Facebook on login. We've already removed a few and plan to optimize it even more in the 5.0.1 release by caching the results of some requests to prevent needing to re-call them in other spots.
For now, I'd recommend trying to disable any JFBC Profile plugins you have enabled and try again. See if that speeds things up at all, and if so, let us know what plugins are enabled and we can investigate why those might be slowing things down so much.
Thanks,
Alex