i've had mixed results with auto frameskips. I've found for me that autoframeskip makes DRMD and Osnes9x actually run worse, wheras LittleJohn runs better. May help Mame though, most the games i've tried, i never played the actual hardware so i wouldn't notice any difference.
sorry but i'd rather have smoother, slightly slower gameplay, than faster choppier gameplay. Best example is any Sonic game on DRMD, play at 156mhz with frameskip 1 and then play with autoframeskip. Frameskip 1 is near perfect and autoframeskip is choppy.