Dan John wrote a great article on Tabatas for T-Nation. In that article he stated that for front squat and thruster tabatas, one should move up in weight when you hit 8 reps on the worst set.
From my expierience this is a good rule of thumb; I can determine if the weight is appropriate based on how I feel during and after the tabata.
I suggest you start doing them regularly and see what works for you. If you are not in a world of hurt by the third set, re-evaluate.