Thanks for the question and thanks also to all those who responded and shared their thoughts.
In my experience, intertial openings tend to cause the greatest wear on lockback knives, since the impact of the blade on the front of the locking bar, over time, tends to peen the face of the bar and change the relationship of the mating parts. Ultimately, this will result in lock failure. I've intertial opened several different high-quality brands of knives "to death" -- meaning that the locks ultimately failed. At that point, I retired the knives (keeping them around to demonstrate the phenomenon in classes, of course) and replaced them with new ones.
Well-made liner locks that compensate properly for wear and start their lives with a good locking engagament tend to be more forgiving and last longer. My original MOD Tempest endured tens of thousands of inertial openings without a problem. Because of its separate locking bar design, when the lock bar moved too far over or I noticed any slight blade play, I readjusted the bar and was back in action within a few minutes. Integral or split liner locks, once worn, cannot be fixed in this way.
If you choose a liner lock, make sure it has a hardened stop pin (if it is a stop pin design). The impact of inertial openings will flatten a soft stop pin and change the lockup. One well-known brand of knives is notorious for this. After I got tired of rotating the pin to compensate for it, I replaced the pin with a piece of hardened drill rod. I then switched to a better knife.
As far as Spyderco's opinion on inertial openings goes, I'm pretty sure that they still consider them to be a form of abuse. Sal has told me straight up that he doesn't particularly like the fact that I teach them, but I consider them an indespensible part of my personal approach to MBC and a viable option for everyone else. As such, I will continue to teach them. As for Spyderco's endorsement of the MBC program, what Sal and Spyderco like best is MBC's commitment to responsible, ethical, and legally defensible self-defense with edged weapons. That's really what they support and endorse. When it comes to inertial openings, we agree to disagree.
The bottom line is that inertial openings can be an excellent method of getting a knife into action quickly. If you choose that method and can make it work under stress, understand that it will cause your knife to wear more quickly. Check your equipment often, maintain it well, and replace it when necessary. I'm sure you'll still find that Spyderco knives and other high-quality brands will still give you great, long service for your money.