It's hard to predict what will happen when you're jailbreaking. Some jailbreaks are designed to preserve the state of your ipod. But you never know when a little something will go wrong and you'll have to reset the ipod, losing all the data and having to set it all up again.
As for waiting for the SDK: With a report about the SDK (if not the SDK itself) only a week away I would agree it's worth waiting.
That said, I'm not sure I'll be giving up my hacks. I have doubts that the touch will allow things like Terminal interfaces to be installed. Maybe I'm wrong and Apple will really open it up. But I'm not willing to give up the ability to install what I choose to install just because Apple has an SDK.
If there's a key application that only works with an unhacked device and others that only work hacked I'll have some hard decisions to make.