Why is iOS 5 draining my battery so fast?
I think I've found the answer for my case. Location services were completely innocent, and I've returned them to default settings. My phone synchronises with a Zimbra server, set up as an Exchange account. The update enabled sync of Reminders, but the Reminder sync didn't work. Removing Reminder sync from the Exchange account setup has stopped the battery level dropping while I watch.

My general advice is to check your mail accounts to see if anything new is being synchronised, and then disable it if you're not using it.

Edit: added image showing Reminders control.