While that is true about the $1.50 surge protectors, there's also a light with a fusee that should have a similar failure level. Or at least that's the theory.... That said, I guess they're probably better than nothing... slightly....
IMHO, a better idea is a UPS. They often have non-MOV surge supression mechanisms that don't have the burn-out problem, and if they do burn out and you lose some attached gear, they usually provide a fairly decent guarantee as far as replacing equipment connected to them. Even better, if you're doing computer recording, it will protect from blackouts, something that a line conditioner won't do. If your supply power is particularly electrically noisy, you might consider buying a high end UPS with built-in line conditioning.
As for line conditioners in general, with modern equipment, it should make no detectable difference (beyond the protection from damage). Electronic equipment down-converts your AC house current to DC prior to actually using it. Generally speaking, any noise in the AC house current should be reduced to an undetectable level in the process, assuming the power supply portion is properly shielded from the rest of the device.
My gut feeling WRT Harplover's gig was that you had a ground loop between two outlets on different circuits, and by plugging the additional gear into the conditioner, that was no longer the case. That said, it is more plausible for line noise to affect the output of a power amp than other equipment, mainly because I've never been inside a power amp that didn't make me want to cry at the lack of shielding. Of course, on the flip side, it might say something about the quality of the gear that I've had to get inside them to begin with, so take that with a grain of salt....
