Ignoring all of the senseless surrender votes that pop up quite often even though both teams are relatively equal in gold, levels and even teamwork; i almost never agree to a surrender even when the match does in fact look like it is already lost.
The match i linked is one of the rare examples of a truly great comeback from a no turrets nexus below 50% situation to a win, all while being behind in gold for pretty much the whole match.
This is not all that common, however, every such match far outweighs the handful of matches where usually no more than ten minutes are saved with an early surrender. I was even tempted to surrender this time because i had a hot meal waiting for me 30minutes into the match but i sticked to my principles and i was rewarded for it.
Like coming back from the brink of death to live another day full throttle, a match like this every now and then is enough to keep me playing a game that i am otherwise very tired of.
I say - NEVER SURRENDER!