If you write web content, this article is worth a look - even if you're not in the business of creating conversion copy. The list of examples just shows the value of reviewing your copy - ideally testing with end users. The impact of a few apparently subtle changes can be enormous.
Michael Aagaard has conducted hundreds of A/B tests - basically revealing one version of a web page to some visitors and another to the rest, then comparing effectiveness.
When you see the improvements in readers undertaking calls to action, it's hard not to take his hard scientific approach.
Warning - This article is likely to upset creative marketing types...
Online Copywriting that Converts: 5 Lessons from 250 A/B Tests - article by Michael Aagaard for contentverve.com