Sample heating is a typical problem in biomolecular solid state NMR. Heating due to spinning depends very much on the spinning speed. For a 3.2 mm rotor at 12 kHz it will be around 10 deg. Fast MAS with tiny rotors of 1.2 mm (~60 kHz ) produces ~ 50 deg of heating. However, a more serious problem is heating during RF irradiation. This might be very severe, and is especially pronounced for samples containing a lot of salt dissolved in your solvent. Usually the problems arise when long high-power decoupling pulses are applied during the sequence (for instance 100 kHz decoupling of protons for 30 ms of acquisition). As I said it might be quite severe, depending on your sample and experiment, but some extra 40-50 deg is not unusual. The best way to deal with it is to compensate heating by extra cooling of the sample. I hope this is helpful.