I've steered clear of POP3 connectors since usng Exchange 2003. I've never had the need to use them. Afterall, I route all my mail through our Exchange Servers. In fact it never occurred to me that you could use this way to get your mail until I saw a couple of our SBS clients using POP3 connectors to collect their mail.
The Microsoft Pop3 connector in SBS 2003 Exhange is very clunky. You've got a two choices for routing mail to mailboxes.
One to one - one pop3 account delivers to one mailbox
One to many - one pop3 account delivers to many mailoxes in the exchange organisation
Having experimented with the One to many type system on SBS 2003, I would recommend using a third party Pop3 connector. That way, you get email downloaded from the pop3 mailboxes and forwarded using the exchange smtp server onto the appropriate mailboxes. We used one from www.quantumsoftware.com.au
Search the pages on msexchange.org for a range of POP3 connectors.