Ivanhoe, there seems to be three "seperate" issues going on:
1) "Squeeze unlocks", whereby your own finger flesh disengages the lock during heavy squeezing. Seems to be related to "twisting motions" in some knives; good grip shape design helps a lot here.
2) "Pressure failures" are as Rich says, steady pressure causing slippage. I have a pair of 5.5" AlMars, possibly the biggest linerlocks ever made - too big, they have a tendency to just "buckle" under pressure. I mean the grips expand, the lock spring plate visibly flexes, etc...I consider it a "slash only" weapon, not a stabber. This kind of "gross warpage" is rare, but in small non-noticable amounts may be a factor in other failures.
3) "Knock failures", whereby slamming the spine even somewhat softly can set up a "shock wave" down the lock spring and pop it loose. Joe Talmadge has more info on this, tonight I'll go dig up threads on Bladeforums and post URLs here.
The strongest lockwork of any folder I own is the Godzilla-strong lockback on the Cold Steel Vaquero Grande. Mind you, it isn't very smooth from the factory - I have a dremel-tool recipe for tuning it that involves rounding out a "pause notch" built into the tang, EMail me for details.
The Axis lock is strong as hell, the old Blackie Collins "Bolt Actions" on such as the Gerber Parabellum was cool, the Sebenza/Pinnacle type "Integral lock" gets STRONGER the tighter you grip it, the REKAT Rolling lock is superb and about to be licensed by Spyderco. MT has a "Microbar" that's interesting if unproven...
Did I miss any? Upshot is, Linerlocks are no longer the kings.