Yea I hate to go against Google especially with IMAP functionality, but I've had POP Gmail configured on my BlackBerry for about 6 months, with 2 different Gmail accounts.
I fiddled with IMAP access on my desktop using Outlook 07 and have had some success with it, only a few minor issue's.
So I then removed one of my Gmail accounts on my BlackBerry and re-added as IMAP, so I've been using IMAP access on my Blackberry for a few days now and as soon as I can I am going back to POP.
IMAP has a bit more delay then POP, I sent the same email to both my accounts and the IMAP account received the email about 2-10 later on. Don' get me wrong now Sync between the BlackBerry is almost instantanious, if I read/delete/ mark as unread my Web Mail interface is updated automatically, however their does not seem to be any Server to BlackBerry Sync, if I read an email on the Web Mail it does not set itself as read on my blackberry.
Bottom line Sync between Client Program and Sever in perfect, between BlackBerry TO server perfect from Server TO BlackBerry non-exsistant, at least in my tests and I have been taking notes