Dear Stats Man,
Great question, and like all great questions it has the same answer, "It depends."
The Key Is Mutual Attraction
I HAVE turned friendship into relationships. Quite frequently in fact. The key was that we were such good friends that it naturally boiled over into other things. Actually, the key really was that in most cases, our friendship was based on mutual attraction.
Depends on the Context:
Context 1: After a Date
However, it depends on how the line was said to you. If you've just gone on a date, the evening was romantic, you've walked her to the door, and are trying to give her a passionate goodnight kiss, and you get the line...that's bad. Pretty unlikely you'll turn that into marriage.
Context 2: After Kissing a Friend
On the other hand. If she's already a friend, you find yourselves alone in a romantic setting, and the kiss happens...then she pulls away and gives you the line...I'd say there's a chance there.
The difference is that in the first case, she's giving you the line to get you away. In the second case she's giving you the line because she's scared of these new feelings and what might happen. It's the second case that is more likely to turn into real romance in my opinion.
Of course, it could be that you're just a really ugly guy! (I'm just teasing!)