Hi Brad,
I recently took the plunge and upgraded 4.1.2 to 5.5
I had to detour via 5.2.1 to start with, but eventually it all worked out. The only problem I had was Webmail, but I just reloaded over the top again and it worked.
I have about 14gig of user data, and it went in no problems..
Hope this helps,
Karl