All good points to think about.
I think that they key worth repeating is, as was mentioned by Tellner, myself, and others earlier, is that there is no magic totem to get you out of a "fight" once you are in one. OC may assist you, but if you can't readily escape, you will still have a "fight" on your hands. You aren't going to spray someone, and they are going to yell "Owee!" and cover their face, and the fight will be over.
Statistically, data shows that OC has been proven as a whole to be
helpful to officers and people trying to handle a violent situation. Anecdotally, there are enough cases of OC failing to work to warrent concern for those who carry it.
Yes, it may be true that anecdotally, OC may cause someone to increase the level of violence (through adrenaline, or anger, etc.). I don't buy the argument proposed by some that one shouldn't carry OC due to this possibility. That is akin to saying "Don't fight back your rapist because he could get angry and assault you more or in a worse way." This is a victims mentality that is insufficient and inherently flawed.
So, I think the main thing to remember is that if one carries OC, then it needs to be used IN CONJUNCTION with another tactic (escape, fighting, etc.). OC is something that will assist you in achieving your goal, but it is not the means that will allow you to reach that goal. Too often people think of OC in one irrational extreme or another; either believing that a .5 Oz. pocket keychain is going to make the attacker drop to his knees in a choking fit, or believing because anecdotally it didn't work in a few cases (15% according to stats) and because there was still some struggle when it did, that the tool is completely useless. Neither extreme is reasonable or true.
Reasonably, one has to realize that once one is "in" a fight, one "has" to fight; and no tool, OC or otherwise, will change that. This is why we need training, and mainly the tools to stay out of the "fight" in the first place.
What I would still like to see (as I'll mention again) is how the use of OC (with proper tactics) fairs for the person trying to escape an attack. There is anecdotal evidence of OC being very helpful for one trying to escape, but I would like to see some clinical trials. To date, we don't have data that I know of regarding this...