Followed these instructions on my 3GS
1- Delete your email account(s) in Settings > Mail, Contacts, Calendars > Your Account > Delete Account
2- Reset Network Settings in Settings > Reset > Reset Network Settings
3- Reboot your phone by holding the sleep/wake (top) button then sliding to off.
4- Re-add the email account Settings > Mail, Contacts, Calendars > Add Account…
5- Turn push back on
And it so far so good. battery consumption is back to normal again. Well slightly higher than on ios 4 but that is to be expected no?
Am running the iPhone as usual, not disabling anything i didn't do on iOS4.
Thanks to HayriC