The biggest issue I see for functional testing is maintenance. I haven’t seen a way of building functional tests that is not staggeringly costly to maintain, both in terms of cost and in time and energy spent by developers on automating them.
I’ve quite a bit of experience in building functional tests in Django with python that I can share with the crowd, and one of my current hats at PlateSpin (my current place of employ) is to lead the charge in building an automated acceptance test framework, which has me running into all sorts of fascinating “people” issues, in additional to the technical challenges. I’d be happy to share those.
I hope to hear the stories and ideas of other people who’ve worked with diverse functional testing tools before, both for immediate benefit in my current quest, and to stimulate my own ideas that might be used to improve the state of the art in functional testing.