We have done studies here at the University of Minnesota that have shown that having milkweed around actually speeds up egg development in females that were overwintering in Mexico. This is a question that scientists are still working to answer. But we don't know how they find the specific spots in Mexico. Personally, I'm not sure that we'll ever be able to answer this one - which I think is kind of nice. A. No, I haven't done this.
People working in the California colonies have, though.
Just recently, Paul Cherubini from CA, made the following statement on the Monarch Watch listserve. I think that unless the rate of logging decreases, future monarch population numbers will be much lower. It is VERY important that the overwintering sites in Mexico are preserved. Of course, it is also VERY important that suitable breeding habitat and migratory routes in the US and Canada are preserved. We all need to work together to ensure that your children will still be able to study monarchs in their classrooms twenty or thirty years from now.