I would HIGHLY recommend signing up for he
BTSC RSS Feeds ...
keep this link handy:
Software Support Life Cycle; generally RIM has the next planned service pack release date up on there.
Lastly, check in here ... I try to get as much info out of our Partner Support Account Manager with RIM with regards to release dates / patches / changes, yadda yadda yadda (as I'm sure most everyone else does), and anything that isn't NDA'd of value gets posted here.