The list I posted is just the top sites for Feb 09. Lots of other date ranges available at that marketing charts site, poke around.
I use this data to compare what a top-converting retailer is doing on their site with what my merchant in the same industry or niche is doing. For example, if my guy is flogging shoes, and the top apparel conversion site is doing things radically differently than my guy, I would adjust my presell flow to bridge the gap.
Say my guy is really low on trust factors on his site, or doesn't articulate his USP well - I make up for that on my presell page and try to pass on a visitor who has that buying need properly addressed. I try to bridge the gap and "pre-close" as best I can to increase my conversion rates.
Looking at what works for others and then applying that to your own campaigns is really useful. Especially for new-to-intermediate marketers, if you add this intelligence to your other datasets & tools, it can turbocharge your campaigns and really save you a lot of time and money in terms of testing costs.
Test test test, that is the key, but testing does take $$, so whatever trims that down is a good tool in my book