Note: At this point I'm using Janrain's Engage identity service to create something consistent out of this flock of outfits.
Engage works quite well but leaves behind an empty "Cross Domain Receiver Page" when used with IE.
Just close (or ignore) that page and all will be well. In the meantime I'll contact Janrain and see when there will be a fix.
If a fix is not forthcoming I'll write my own handlers.
