No matter what, I play it out until I'm REALLY on the ropes. Losing a settler at the beginning or popping a major barbie-hut next to my only city can be frustrating, but it only adds to the fun of the game--after all, CIV is a quasi-historical civilization simulator, and the interesting thing in history for me is how different tribes managed to overcome their particular handicaps to survive.
But yeah, I've lost two or three times when I kept thinking: "I'll just take a couple more cities, THEN I'll switch my production to SS-building..." When I've lost, these have been my famous last words.
For those of you who quit early because you lost a settler, or even a city or two, I can only say that, in my opinion, you're missing out on the best part of the game! It's all about survival!
Except for the recent GOTMs, for the past two years I've only ever played Deity level, with 7 civs, large map, and all other settings on random. I've paid no attention at all to my score, and whether I've managed to max out my population, until the game has been effectively finished (ie, I KNOW I'm going to win). It's difficult, and I've been pretty unlucky a few times with terrain and starting location, etc, but it's so much more satisfying that way.
Mind you, I haven't played a human opponent yet, but I hope to this summer. Actually, it sounds like I'm in the same situation as you, Shadowdale, when it comes to current living arrangements.
