714gorilla:
I did a lot of the same exact research and also noted very little help in promoting as well. In fact I had one sponsored promotion for a very popular item, for over 3 months straight, that never showed having received a single click (thus it must have been WAY down on the search results). I think they also employ a location based algorithm (or more likely it is inherent in the shipping price difference part of the Best Match algo) that make the displayed results vary considerably, especially in competitive areas, so you can't always go by your own search results either (unless you do a search through a remote proxy server.) Thus for shippers from out of the country, with cheap subsidized shipping , it works into the algo, pretty much regardless of where you are in the US, to be a major factor in the higher rankings.
I HAVE noticed SOME positive influence for Top Ranked badges over non-badged listing, but it seems to fluctuate, like maybe they haven't locked in the ideal settings yet. It would also be interesting to know if the Half-A$$d "tracking" provided by other country mail services count as valid tracking on-time tracking for Eb or if they simply give them an automatic free ride on positive ontime tracking and delivery ranking.
Other factors that are well known to affect Best Match rank are of course, keywords (there's something to be said for long-tail results though) and your sales conversion ratio, on a per item basis (so if they were first to market with lots of sales, generate a dozen fake sales or cheap promotion sales of their items they get bumped to higher position).
