If you use Gmail's Mail Fetcher tool to grab email from other POP3-enabled email accounts, you may have noticed that it sometimes checks for new mail on very slow intervals—particularly if you're importing from a mostly inactive account.
Weblog TINYenormous explains:
This hack might not be for everyone, but if you have Gmail set up to check your pop accounts, [Google doesn't]let you set the polling frequency anywhere. This can be bad because it makes you go to the settings page [if you want]to hit the refresh button on each one of your accounts! After a little digging it turns out it uses a weird formula to determine the polling frequency. Let's say it checks your account and finds an email. The next time it checks it will wait for _slightly less time_ before it checks again. If it finds email a second time it will continue to shorten the interval until it is checking every 5 minutes or so (maybe even less!). The purpose of this is so that Google doesn't waste resources checking an account that only gets one email a month.
The downside of this approach is that if you are eagerly waiting for that one email you might be waiting for a long time (i have seen wait times up to 58 minutes!)
The solution, then? Your account needs to get more email. Naturally, though, you don't want to flood your Gmail inbox with new email just so you can be sure your POP account is checking at more reasonable intervals. The post suggests setting up some Terminal scripts with Automator to send your POP account emails on a regular basis, then filtering out those emails when they hit Gmail so you never have to deal with them.
If you're not on OS X or you don't love the Automator idea, you could probably offload the frequent emailing duties to some other web service. An active Google Group seems like a good option; you could sign up for the group, set the Google Group to send emails for all new posts, and then just filter the Google Group email out when it hits your Gmail inbox (via the POP inbox).
If you give this a try—or if you've developed your own methods for overcoming the slow POP check—let's hear about it in the comments.