I find that for the most popular search phrases, the top 5 pages or so vary almost erratically. In-fact to the point of being almost useless.
It can be exciting to look through your web-stats and see a came from Google page #1 result but if this thread shows anything its that you may not be in the same place when you look again. Obviously your local will have an effect but with searches returning several million results, do you really expect to stay there using any strategy unless you're as commonly known as e-bay?
Household names are almost as important as keyword placement and content in my view. You simply can't compete with the volume of Internet users that type anywhere online about eBay or you-tube. #5 one day, #70 the next, unless you have a particularly unique site, but web directories are simply common.