The SDK will be used by developers to make software for the touch that will be downloaded through iTunes (most likely) and will be for a certain fee...but these apps will be Apple supported and iPod safe with little chance of breaking your iPod down.
So if you jailbreak, you have a risk. If you don't and use the iTunes route, you have to pay more but it may well be worth it.
Some developers may make Apps for free, like Google or AOL