I am BES activated and have two BIS accounts. I can send email to both addresses from a PC and receive those messages on my Storm within a few minutes of them being sent. One account is POP and another is IMAP. The IMAP is pretty much within a minute and the POP is within 3 minutes.
The BIS on the Storm seems to be operating much the same way my 8703 and 7250 worked. Hope my brief .02 helps you determine where the issues are on your end.