I recently acquired a 2002 Rubicon. It ran fine at purchase. When I changed the oil, I pulled out 2 and one half gallons!!!! The specs call for 5.2 quarts. So far I have detected no functional issues with the quad. Any thoughts as to the engine damage I might be looking at? How did the quad function with twice the oil? What should I be checking? Thanks  

the main issue with overfilling is that the oil can end up in the exhaust.

as well with that much oil in it you may have some issues with seals leaking.
more oil = more oil pressure on the seals.

as long as you have no problems now then i wouldn't sweat it, but i would for a while check the oil level to be sure it isn't leaking anywhere.