jr - i was having the EXACT same issue that you were having. i was popping the email, per gmail's instructions. instead of popping the mail, i just did the forwarding thing per stinsonddog's site and everything is working fine now. forwarding is realtime whereas the popping had @ 15 min delay and the duplication thing. over 1000 emails in 8 hours!!!
ur filter in gmail should b forwarding
to
. this allows any incoming mail to be forwarded to your BB.
in the BIS, you should have your auto BCC (Profile > Auto BCC) set up to go to
. this allows you to have a copy of your sent email in your gmail acct.
it's setup this way so that when u reply via BB to a gmail email, it won't send u a duplicate notification on your BB since it's BCC'ing your gmail acct. gmail will foward mail to the BB ONLY if your email address is in the TO: field. ALSO, deleting the email on your BB will delete the emails on your BIS acct but NOT in your gmail acct.
hope this makes sense to you. basically, setup the ONE filter in gmail and your Auto BCC in the BIS. DONE.