I didn't and it's nothing jailbreak related - it's for a problem related with tethering and unsupported phone carriers on (legitimately) unlocked phones.
i downloaded canabalt not realising it needed 3.1+ (silly sure )- i have a legit 3GS 0n 3.0 but have heard that 3.1+ has issues - true?
I can't speak for other models but 3.0, 3.1 and 3.1.2 have all been perfect on my Touch 2G. Apparently 3.1.2 fixes some bugs in 3.1 so I guess that helps. As for Canabalt, it uses a v-sync option that isn't available on 3.0. The dev said it's possible he could optimize the game enough to get it to perform just as well without using it... but it'd just take more time that could be better spent on updates/other projects. He didn't confirm whether or not he'd be doing it.