To me, Camping/Ambushing depends on the game, and there are some games that, i think, spawncamping is fine. However, those games where i accept spawn camping are the FPS where there is a "Spawn Shield" as a preventative measure to continuously destroying someone the second their screen turns into the game. There's nothing more annoying, i find, than ending a loading screen with a nice blood red screen and my character falling to the ground. But with Spawn Shield, i consider it fair game. If i'm able to get into your spawn and kill people that have a 5 second invulnerability, not my fault, you had plenty of time to react, i'm just sneakier
Note: In my opinion, for spawn camping to be even considerably fair, two conditions should be within the game itself, Spawn Shield, and a set "Base Spawn," not that random placement, conditional spawn, i've never liked random spawn because spawning in the middle of my enemy is most frustrating when i'm surrounded, kill one guy, get flanked from 18 sides and pummeled into the ground like an anorexic band geek in the gym locker room making comments on someone's mother.
Now that i've addressed spawncamping onwards to regular ol' ambushing. I personally love it, i don't resort to it every time because there are cases when one must camp to survive and ultimately win, and other cases when rushing and, as i do enjoy calling it, "Base Raping." The act of camping, is a preventative measure against said base rape. Without a strategic placement and a keen eye, you have the crazy berserk rushers that get into one's base and destroy every living thing including the kitten and his mittens, and quite possibly the pet rock. When i surprise someone who normally is all run-n-gun from a random obscure place in my very own base, i like to utter something along the lines of "Welcome to MY base ^_^ Now get out!" After all, what a house warming party without the welcoming party ^_~
Quick Summary:
Spawn camping = can be ok depends on conditions of the game, most situations you're a jerk for doing it.
Ambushing = Anti-Rush, Legitimate, i'm ok with it, even when it frustrates me.
Base Raping = Fun ^_^ ... Well... Wun for me... Was it good for you too baby? ^_~