We had the Dutch Open last weekend and as far as I knew nobody flew through the NOTAMed SRZ (which included the holding and box, obviously)
It helped that this SRZ was located into another, permanent SRZ which is almost completely contained in class A starting at 1500' and up (so no en-route traffic possible, only traffic climbing up from underneath), and that Lelystad Radio always mentioned "aerobatics active" to everyone who asked for airfield information. Also Lelystad has no overhead joins but a specific, mandatory joining procedure located on the opposite side from where we did the competition.
There were a few banner towing aircraft who used "our" frequency (which was in the NOTAM as well) to coordinate their towing and general chitchat. Fortunately they found another frequency after a polite request.
So great weekend, great weather, no incidents (and I came in 1st in the Beginners class
).
(Oh, and before anyone starts to make smart remarks about aerobatics on an IFR flightplan: The permanent SRZ is carved out of class A airspace which effectively becomes class G airspace in favourable weather conditions. It is there to allow aerobatics, stall practice and a few other things for which you need more than 1500' in altitude, roughly above the busiest GA airfield in the Netherlands.)