My husband has used SPD-SLs for about 100,000 km without a problem.

My experience with them - three different pairs, including one 105 and two Ultegra - was miserable. Mine had the issues you mention clipping out (and sometimes in as well, although it was less of a problem), would not work properly in wet weather (an issue in the PNW!) and as soon as the cleats got a little worn they'd be even worse. Go figure. I think their quality control is a bit hit and miss on pedals.

That was about 4 years ago. I have since returned to mountain SPD pedals with super-stiff mountain shoes (Sidi Dominators) and I couldn't be happier.