Mistwell
Crusty Old Meatwad
I guess by rule the is NO Opportunity Attack from Prone to Standing, since there is no movement OUT of a square, we have House Ruled that standing DOES draw OA's.
We've found this makes attacks that cause the Prone condition in melee much more exciting. Otherwise they're kinda lame.
Then woe unto you if you allow the Polearm Momentum feat in your game from Martial Powers. I can think of a combination that, with your houserule, would result in foes never getting back up once they are knocked down.