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.

Update: check out this paper about heating effects in lipid membranes http://www.ncbi.nlm.nih.gov/pubmed/15366061

This is also a critical problem for MAS-NMR of paramagnetic species since the spectra are useless without the actual temperature in rotor. For high spinning rates (60kHz),we measured a 47°C difference between our controle unit and our actual temperature on one of our samples. We use NiCp2 as an NMR thermometer to know exactly the temperature inside the rotor.

yes, it seems we met the same phenomenon, when there is the nano-tubes in the sample.