Masochism - Yes or No?

Not much. I have seen Olias using it and saccing himself to death when he was already at low health, with both my healers and all the enemies dead. Perhaps he was trying to cast PS on himself then with Masochism on and murdered himself in the process. I have had some survivability issues with it as well so I stopped using it.

I've just been testing it a little, but my reasoning is based on this:
1. It seems to make MM's fall behind the team more.
2. Bar compression, what else could I take? (This is really the importaint one)
3. How much damage does it really add in practice?

That said, I'm still using it on most of my chars. I'm mostly just curious of what I actually loose by not doing so? Bar compression would be a valid argument if there were good replacements, but what else is there to use? Besides, the standard MM bar already has a free slot (Putrid Bile).

Bar compression would be a valid argument if there were good replacements, but what else is there to use? Besides, the standard MM bar already has a free slot (Putrid Bile). You'd seriously loose Putrid Bile before Masochism? O.o

You'd seriously loose Putrid Bile before Masochism? O.o I would choose both masochism and deathly swarm over putrid bile (which is exactly what I do). Putrid bile is not reliable and I have no idea why its still on the mainbar of the wiki build.

I have had some survivability issues with it as well so I stopped using it. Most of the time, Masochism works out fine. Maybe it is just me, but I don't feel a big difference with or without Masochism on my MM bar since my mesmers kill so much faster than the minions do and with so many spirits, my team can usually survive well even if all the minions are dead. But like I said, I take it because I have not found a better alternative.

If you are having survivability issues with your MM, try fitting in blood bond. It works well with masochism. With a superior death magic rune and masochism, my MM is frequently the favorite target, but blood bond balances all these away very well and helps redirect damage to the minions making them explode more.

I usually prefer another utility from a secondary profession in that slot. That is fine. Your MM is not going to fail just because you don't bring Masochism.

Masochism is usually a good choice and there are not many better alternatives in most MM builds. But I wouldn't say that all possible MM builds under the sun must bring along Masochism to be optimal.

Exponential? The gains of any increase in attributes are usually, at best, linear. The skill is still worth it. Health + Armor = exponential, as they multiply together to find the total durability (technically quadratic at n^2 if you want to be mathematically precise). Damage per hit increase is supralinear as well (technically quadratic again but the quadratic factor is very small). Total damage dealt before death in a battle is therefore approximately cubic (n^3).

Example: A Bone Horror @ Death Magic 0 vs 10 vs 20. To calculate damage before death lets just presume that our average minion is suffering 40 DPS in battle with no healing (just made this number up for demonstration purposes). Note that I don't know the actual average damage a minion deals out since there is an unknown random crit rate involved and the wiki just gives the total damage range. I'll go test and update these numbers later, though I doubt I'm off by much.

100 health and 9 armor = 41 effective health, 1 damage per hit. Damage before death = .33

320 health and 50 armor = 269 effective health, ~16 damage per hit. Damage before death = 33.9

520 health and 88 armor = 844 effective health, ~ 37 damage per hit. Damage before death = 246.3

Compare to Flare which offers a mere 20/50/80 at the same attributes. Pretty much every skill in the game increases linearly except for those skills that have multiple linearly increasing factors that multiply each other. Besides Minion skills, Splinter Weapon (20/560/1560 potential damage), Protective Bond (6/4/2 energy per hit), and spirits (health/armor increases + defensive spirits health loss per activation decreases as well) are good examples.

EDIT: My tests (N=57) show that r10 bone horrors deal 15.5 damage per hit and r20 bone horrors deals 37.1 damage per hit. Wow, I was close in my prior estimate.

Health has a linear effect on durability, armor a logarithmic. The product is far from exponential. Sorry, I was mistaken before. Linear increases in armor give exponential effects. Certainly not logarithmic, which is even worse than linear. Damage taken is the log of the armor, which means the inverse (damage before death) is exponential.

+40 armor = 100% more durability
+80 armor = 200%
+120 armor = 400%

Of course it can be argued that durability is sub-exponential when you take into account that some damage you face is armor ignoring. Furthermore, whatever growth rate it technically is doesn't matter much since we are only interested in a very small section of the function anyway (16-19), not extrapolating things to infinity.

And yeah, with EBSoH + OoU minions are hitting almost 70 damage per hit, which translates into over 800 DPS if you have 22 bone fiends (though chances are you have at least a few vamps/horrors). Even against warriors with 100 armor they are hitting 55 damage per hit. God forbid using Volfen Blessing to give all your minions +33% IAS as well, GW should immediately stop and tell you that you have won the game when you reach 1200 DPS.