It's considered a seminal text among copy writers. I found it very helpful, for exactly this purpose.
But he talks about direct response ads, which can be seen in light of A/B testing, on web pages. For example, by changing one word, the response rate was increased 20-30%.
I earnestly don't think it's that different a beast. The techniques always remain the same, so why not learn from the master?
For more recently written stuff, I think groupon do a really good job, and you can find their stuff online: https://docs.google.com/View?id=dmv9rbh_11gtqx983t