If I'm logged in when I perform a Google search, and I click on one of the results, then next time that website appears in search results Google shows me the time of my most recent visit.

For sites that I visited today, it's just the time of day in local time. Otherwise it's just the date. If I've clicked the same link more than once, Google tells me this, e.g. "3 visits – 2.40pm".

I've not noticed this before. Is it new? How will it help me? Will it help Google to become all-knowing?

If it's not clear what I mean, there's a screenshot here:

http://web-owls.com/2006/05/12/google-knows-all/

Yes, this has been around for a while. It's a search history/ personalized search feature. Not sure exactly what it's good for... I guess it aids your memory :)

Yeah I've seen it many times before.