I was in a game where the DM wanted to grind us through. 30 combats, ending with Orcus. We made it to level 7. It was a lot of fun, but things definitely didn't go the way that he expected them to. He originally thought that they would take 5 or 10 minutes per combat. I laughed at him. I started calling off the hours about 3 hours and 4 levels into it.
There was a lot of cool stuff happening all around. I wish that I had been able to hit more often, but things were pretty nifty.