If some place is already mapped, please do not blindly "improve" it by re-adjusting everything to Yahoo imagery. It might be that someone spent a lot of time re-, re- and rewalking those paths and that the images are not aligned correctly.
Argh. ARGH. AARRRRGGRGHRHRH!
edit: Is there someone from Yahoo in the community and easily reachable? At Yahoo's maps page there is a feedback link but it requires an Yahoo account (morons...).