My highest combo so far is 3,800,000. I know I'm capable of getting atleast 5 million pretty easily. Although, I met this one kid who got 225 million without cheats. I witnessed it myself. He had a huge line that went all over the level Downtown and he kept repeating it.
If you are having trouble getting high scores here are some tips.
--Try to use all the moves in your combo. Do some air specials, some lip specials, some grind special, and some manual specials.
--Usually a bowl works the best for getting a high combo because you can start with some air tricks, then when you aren't getting as much air do a lip special then start grinding on the edge of the bowl. After it becomes hard to balance start doing a manual in the middle of the bowl.
--Try to find a rail that has something you can sticker slap at the end...that way you can sticker slap and ride the rail again, thus increasing your score and multiplier.
--Do manual flatland tricks to increase your score multiplier.
--Load your specials with a bunch of different grind tricks that way you get more points.
--When you think your done, jump of your board and start spraypainting the ground, this will increas the multiplier and increase your score by 3,000.
I hope some of these tips help.
Save me Jebus!