Oh, not to mention the horrors that come from Improved Grab and Swallow Whole, both of which use the grapple mechanic... (And this is, more or less, a personal experience.)
DM: Alright, so the shark has bitten you and you failed two consecutive grapple checks, so you're in its stomach. You take 24 points of damage from the bite, and 16 points of damage from the acid in its stomach. Your turn.
Me: Great. I'm gonna cut my way out with my sword.
DM: Ooh, that's a two-handed weapon. You can't use that.
Me: Dang it! Alright, I'm gonna try to climb out.
DM: Make a grapple check.
Me: (Rolls) *Sigh* I failed. I'll try again. (Rolls) Alright! I rolled really well.
DM: Alright, you made it!
Me: Awesome! I'm gonna swim away.
DM: No, you're still in its mouth.
Me: .....
DM: Alright, its turn. It got a 45 on its grapple check. You're back in its stomach. Oh, and you take another 20 points of damage.
Me: Alright... I'm, uh, gonna try to get out again. (Rolls, and fails. Rolls again, and fails.)
A couple turns pass. My character is close to dead.
Me: Alright, I need to roll really high, and it needs to roll really low. Uh... twice. (Rolls, and, amazingly, succeeds. Twice.) YES!!!
DM: Good job! You're out of its mouth. Now it's taking its turn. (Rolls) It hits you. Make another grapple check.
Me: (Fails)
DM: Alright, you're back in its stomach...