The global recruitment forums recently underwent an upgrade, where the forums were split into Alliance and Horde factions. This has helped a bit with the number of posts per day, and has thus lessened the number of required bumps a recruitment posts needs to keep it on the front page.
However, you still have to bump it quite a bit.
I've found that a post falls off the front page of the recruitment forums about every two to three hours. This means that if you want your guild to have high visibility when recruiting, someone needs to be there every few hours to bump it back up.
This often falls to the officers of the guild to do the bumping. However that doesn't always look the best. It's often helpful to have other guild mates bump the posts too. It shows that the guild is involved in the management and recruitment of people, and that everyone cares (not that there aren't other ways to show this).
So get out there and do yourself a favor! Bump those recruitment posts!