I'm seeing something similar. Two computers, on the same Internet IP, neither with any kind of malware or anything, bringing up completely different search results. I don't think there are different (aside from the various countries) Googles, but I think Google is trying to tailor the rankings to something. Hell if I know what, though.
Search engine optimization. My site, for one keyword, is ranking 62 on one computer, 24 on another, and 60 according to an external ranking checker. WTF?