Never a good idea, unless you want people to give you money via credit card. From my experience, having one of those badges on your checkout form results in a measurable increase in conversions, even if it doesn't mean anything to people who understand security.
I doubt that this is the case. I'd expect to see it on a lot more sites were it true. I'm guessing some other factor created your measurable increase. Willing to be proven otherwise though.
I would love to see an A/B comparison of this. For me, if I see those badges, I assume the site doesn't know what they are doing, as they should know, any GoDaddy automated scanner is not worth the wasted disk space from the hits in your httpd logs. Any programmer that aspires to show those logos is dangerous and that site will not get my personal information.
