i've never used them, tho i've traveled quite a bit. however, using them would not have saved me from the 2 instances of (minor) damage to my boards i've experienced.
the first (in 2007) was what looked to be a suitcase corner came down on the bottom of my board. straight down. the result was a small, fingernail-sized ding. it was up beyond where the nose/tail guards would cover. i think this was the result of poor/rushed packing on my part.
the second was this passed summer, coming home from the maldives. a suitcase (again) looks to have scrapped along the bottom on my board for a good 12-18" or so, again in the area not protected by the guards. this, happily, resulted only in a pressure ding. while the board in question is my current magic board, it has seen a fair amount of abuse & is nearly ready for retirement, so i wasn't too fussed about it.
the point being, i've seen only 1 crushed nose (the result of my father forcing a too-long board into his coffin bag against his better judgment) & 0 crushed tails in my travels. i think if you pack well, & protect the rails (really the only truly vulnerable area i can see in most bags), then you'll be fine. the key is to consciously pack well.