Someone on the SMB claims that someone he knows who went on the pitch is banned for the rest of the season.
It is a problem but I'm not sure how it can best be dealt with. If the club received a hefty fine, Quinn and Keane could make sure the fans know that by running on the pitch, they're halting the club's progress in terms of spending more on players. However, I really doubt the intelligence of the people who do run on the pitch would understand that, so it would make no difference.
Haven't been to the SoL in ages so not sure if it's always from the same parts of the ground - if it is, increased stewarding along the front would surely be the best solution.