I don't think that's what's happening. I wondered about that too when I was on the earlier leaks. Under gingerbread, fast boot made a world of difference but I never used it because of the side effects. Under ICS, I noticed that the boot times were much improved and so I began to wonder if the switch for fast boot was broken. I did some additional testing that included pulling the battery. The phone still boots in roughly 90 seconds with or without fast boot checked, and returns the same times starting from a pulled battery.. again, with or without fast boot checked.
Since my Thunderbolt days, I've never left fast boot checked. I concluded turning it on for the Rezound didn't have any benefit, so I still don't use to this day. For my part, this is more proof ICS really cleaned up a few issues with Android.