A few weeks ago I tested vinegar as a weedkiller in my "Dealing With Weeds" post.
This is what the weeds looked like before I sprayed them.
I sprayed all the weeds in my walk and drive with vinegar and waited. The next day many looked dead and the grass was turning brown, so it did affect them. It did not, however, kill them. It rained about two days later and a lot of the grass and weeds came back.
This is what they looked like a week later. Smaller but still there, green and growing.
Maybe I didn't saturate them enough? I don't know. I think my mother in law told me that she pours it on the plants that grow on her driveway to kill them. Maybe the vinegar should be poured on the plant rather than sprayed lightly on the leaves? I will talk with her further.
I have not yet used it on the big weeds. I may try that this weekend.