In a earlier thread, i noted that bets using psuedorandom values based on blockchain hashes can be affected by miners colluding with one of the gamblers. Basically if they have a winning block they can withold it. I also suggested a solution.(which i am sure many others would also have suggested, unless i am wrong, of course) (https://forum.ethereum.org/discussion/comment/2758/#Comment_2758
Trying to calculate when the payout is good enough for miners to collude, i realized that the miners might not entirely withhold the block. They might also offer it the moment they see another potential block winner, depending if the bet went better/worse on the other block.(the whole point to wait is to see that) If they put it out there once they see it, and have enough eyes on the network to spot an adversary block, their block might still win.
In principle the order contracts are executed can affect the outcome, and people could put bounties for miners on that to.
I dont know what extent this is a problem. These actions are inhibited by the reward miners risk losing in their behavior, but with a 1 minute block time the reward in a block may be outstripped by transactions offering rewards. To be honest, dont know enough about GHOST and uncles, possibly it gives some protection, though my impression about uncles might actually save some of the block reward for colluding miners. Either way, it brings up that things can be connected this way.
Aside; i'll put the miner collusion calculation on the wiki later.(start a forum topic on it if you want)