Length is clearly an issue with some women. It is not unusual for them to express some uncertainty up front, real or not, and you also hear a lot of the "I guess I'll have to get used to it," as well. Only a few times it actually turned out to be something that contributed to the end of the relationship.
One woman, in particular, really openly struggle with my size, but it seemed to be within a whole slew of sexual hang ups. For instance, she would never let you see her naked. Sex was always under blankets, probably with her wearing most of her pajamas. She really never was really able to relax and I think this contributed a lot to the issue. She was also kind of a crazy drama queen, She even wrote me this sad email about sex and how she was going to learn to be fine with my size. It was part of a long email where she tried to explain why she was such a lousy lay. Anyway, one of my friends started fucking her, so they both exited my life shortly thereafter.
Recently, I had the opportunity to hook up with an ex on a couple of occasions. She invited me over a week or so ago and I broached the subject of a quicky. She told me that she wasn't actually up for sex with me because it was too big a commitment. Too messy, sore after, probably have to shower. Her exact words were something like "It's not like you are selfish, but sex with you is automatically about your size. Most of the time I'd rather just have a lot less."
On the other side, I was driving a date home a few weeks ago and she blurted out "You totally destroyed my pussy. I still can't believe how deep you go. But every time I thought I was going to have to tap out, I started to come like crazy, so I let you keep going." She sent me a picture from work the later day using a customer's crutches as a prop.
There are a lot of factors to sexual compatibility. There is an undeniable novelty in penis size, but there is a reasonable percentage of women who find average sizes work better for them.