It's like +1 it everyday.
don't really like that members can praise their own guilds, though they could just leave and hit praise guild if you changed that, but I think the system itself is kinda bad, zerg guilds will ALWAYS be on top of praise guild even if only half their members remember to do it.
On my server the smaller guilds that actually know each other, play together, and care about making the guild the best it can be have the most amount of praise. The large zerg guilds that don't know who each other are and don't care as much about the guild, don't have as much praise.
You know, no one actually answered OP's question and explained what it's purpose is. I'd like to know too; I figure it has something to do with the political system or something.
"Praise Guild" is used to add a +1 "this guild is awesome" thing to said guild.
Basically it's only purpose is when you go to your social tab, then "Guilds on Server" guilds who have more praise show at the top of the list.