Guys, this is a standard legal "grey area".
If I were you, I would put the images onto your website with a disclaimer with each image that were downloaded and copied from Ancestry.com. Then add a small button linking to Ancestry.com next to the image on your website, and say that for "more genealogical records, visit Ancestry.com.
Even IF, and I mean _IF_ they threaten legal action, keep a copy of the link to THIS discussion thread on the Ancestry.com forums, so Ancestry.com knows strait up you TRIED AND TRIED AND TRIED to get a response from them regarding the legality of posting images from their site, and they NEVER NEVER NEVER NEVER responded. That is a damned good defense legally, as it showed that you TRIED to get an answer.
And in the end, the worst that would happen is they ask you to remove the images or they would take legal action, in which case just comply and remove the images.
And hell, the fact that NO ANCESTRY.COM STAFF EVEN POSTED IN THIS THREAD proves that they dont give a shit. And even if they did, they are obviously too damn lazy to check every genealogical website on the internet to find YOUR webpage with a couple of individual census record scans of theirs.
I say go ahead and post them.