For some reason first time girls get weirded out and come to the conclusion that they dont like it before they even try. I'm a strong believer that every girl enjoys anal even if they don't perticularly enjoy it too much the first few times. I've had girls that hated the idea and actually ask for it now. Girls if your curious give it a go, even if your not try it out and I gaurentee you'll like it. The way I see girls getting analed and get off to it so much it must feel good.
I like saving it for special ocassions. Also, it's not always the right time for anal, and too much use can stretch it out too much I've heard.
I don't think it can be stretched out too much. I fuck my wife in the ass nearly every time we have sex and she hasn't mentioned any problems at all. She actually prefers to get it up the ass.