I have two gmail accounts: one good one and one for junk-mail (signing up for trials/whatever on the internet). I also use the one provided by my university (my employer) but it's a horrible Exchange 2007 server with no IMAP access, so I have to have gmail check check that account via POP3.

In order to get gmail to check my POP3 account regularly, I use cron to send a dummy email to that account every 10 minutes. The dummy e-mail immediately gets deleted, but google's algorithms check POP3 with a frequency dictated by how frequently you recieve e-mails. Without this set-up it sometimes goes 1 hour before it checks the POP3 account. Using this set-up it checks every ~3-5 minutes which is sufficiently fast. I sure wish my university would just give me IMAP access, though.