Looking at logs on my cvsync mirror, I see a few people are syncing at quite short intervals. I guess the same might apply to users of other mirrors too. There's no point updating more often than the interval shown in http://www.openbsd.org/cvsync.html as you won't get updates any more quickly.
In particular there is no point syncing every 15 minutes when it takes you 10 minutes to send the 7-8MB of data needed for a cvsync run (to get just 250 bytes back if there were no changes ;-)
