Looks like th 2 way sync of messages is being turned on sporadically for BB users with gmail accounts. This means your read/unread status of messages and sent items should match up. Will probably depend on carrier/model/OS as far as how well it works and when it gets turned on for you. It isn’t currently working for me on TMO in STL with Pearl running 4.5.

UPDATE: It is working after I reset my mail account (it was still set with BIS previous to 2.6). After recreating it and my filters the sync is working 1.5 way.

Sent items show as sent items on my BB and read items on my BB show as read items in Gmail. Read items in gmail still show as unread on BB. Still - much better than it used to be.