In our Pirate campaign, we're travelling to the Isle of Dread (yes, THE Isle of Dread). You'd be surprised how many tentacular sea beasties and killer vines are out there. I'm praying for dinosaurs right about now.
Often, particularly at higher levels or for monks. Of course, there's Evard's Black Tentacles as well, and monsters with improved grab are a dime a dozen. Not every combat, but very often.
I use grapple frequently, but as I had mentioned in the Trip thread, I am playing a Monk that is a master of all forms of combat, so he has most of the Improved this or that.
Being a Goliath doesn't hurt for grapple checks either.
When I'm DMing grapples rarely happen as I find that grapples while good from a DM point of view are a pain in the backside for players.
In an Eberron game I'm playing in we went through about four sessions in a row where we ran into big beasties with improoved grapple. My warforged Fighter/Juggernaut was grabbed everytime and I just sat back and resigned myself to being out of the fight, which was pretty much the case.