Some good comments at accessify.com about screen reader testing tools:
Some good points were also raised about sighted developers using screen readers for testing
Adrian Higginbotham: Personally I never recommend anyone to try testing a site with a screenreader product unless they are already a confident screenreader user. you simply don’t use the tool in the same way
Adam Perry: I am sure Adrians comments are correct: a Visually Impaired (VI?) person will use the screen reader in a very different way. Nevertheless I found using a screen reader helped to identify areas of HTML which require improvement (inadequate or missing ALT, TITLE and SUMMARY attributes, for instance).