Lots of good comments on this issue, but I feel the need to clarify a few issues.  First, there seems to be a consensus that EI provides a "hotter and longer" spark.  sometimes true, but the most common EI product is a capacitive discharge (CD) system.  The inductive (Kettering) system stores energy by using the inductance of the ignition coil and the spark occurs when the current in the primary is interrupted.  These system, which include magnetos, are characterized by having a relatively slow voltage rise time, but a fairly long spark duration at a low current level.  A CD system stores energy at high voltage in a capacitor and the spark occurs when this is discharged into the coil.  Since the coil isn't required to store the total spark energy it can be smaller and of lower inductance.  The result is a very fast rise time, high spark current and a very short duration.  A short-duration spark works fine as long as there is a combustible mixture in the spark gap at the moment of the spark.  CD systems work very well in engines that tend to foul plugs, which is why their initial popularity was in 2-stroke engines, but they typically don't work very well in engines that operate with "poor" mixture preparation, such as automotive engines running a lot of EGR.  I see no problem using CD technology in aircraft engines as we don't typically operate at very light loads with EGR, except at idle.  The CD system is far more electronically complex than an inductive system, which only requires an electronic switch to activate the coil.  The automotive guys have spent billions researching ignition systems with the result that all automotive engines worldwide still use the original Kettering inductive system.  The CD coils weigh less, but the electronics weigh more.  I agree with Walter that the higher spark current will result in a faster initial burn, creating an effective timing advance compared to a conventional system.

Gary Casey