A few apparent bugs that I've seen so far:
1) No matter how gently I land with a jetpack, I take full damage from the amount of distance I've 'fallen' downwards during my flight time.
1b) Rubber boots did nothing to negate the damage and quantum boots only worked in the overworld, nothing negated fall damage in the nether. I'm not sure if this indicates a bug in the boots or if it's merely a side-effect of the jetpack.
2) Any item with modes don't repsond to the key that would normally change their mode. I've tried this with Jetpacks, Electric Wrenches and Mining Lasers.
Appoligises if theses were already know for SMP, I usualy test the single player side of things.