Maybe a too simple question, but what is the impact of KeepAlive On or Off, for visitors, for robots.
Fact is it was turned off some time ago without my knowledge, and for some weeks my traffic has gone down, and more worrying, on google my pages have dropped substantially down the index. Could there be a connection?
Disabling KeepAlive will result in your site taking up to twice as long to load a page with lots of images. Not good for visitors. See Apache KeepAlive and MaxKeepAliveRequests documentation.
I suspect your traffic is down mostly because your Google search positions are down, but a slow-loading site won't help. Analyzing your log data should tell you if this is true... If Google referrals are way down, but Yahoo and MSN are stable, then it's a drop in Google search causing the drop in traffic. And the drop in Google search rankings is likely due to Google's current algorithm and weighting factors, and not to KeepAlive settings.
As to whether search engine robots might prefer sites with KeepAlive, I can only guess. And I'd guess not; Since most of them don't load the images along with the page, KeepAlive shouldn't make that much difference to them.