I have my wife send emails to my @tmo.blackberry.net when it's a message she wants me to receive right away. I get these emails usually within less than 1 minute after she sends them. Emails sent to my integrated POP3 accounts take around 15 minutes or so to arrive.
I integrate the POP3 accounts rather than having copies forwarded to my @tmo.blackberry.net address so that I can take advantage of deleting some of the messages back on the mailbox (spam, etc.), and so that replies look like they're coming from the correct account.
On a related subject, I've always wondered when I delete @tmo.blackberry.net emails just "On Handheld" instead of "On Mailbox & Handheld", do they stay on a server somewhere where they could be retrieved through other means?