Once up on a time, it seemed that Google and Apple were natural partners, as inseparable as . . . well, two boards of directors with the same guy on them. And then last August, Google CEO Eric Schmidt left the Apple board, citing “core business conflicts.” Those conflicts have become more apparent over the intervening six months as Google has unveiled a smartphone/superphone set to compete against the iPhone.

And Apple may be set to fight back. Last month, they were apparently thinking about making Bing the default search engine on the iPhone, and now people are speculating that Apple is contemplating Bing for the iPad. You know what they say about the enemy of my enemy, but . . . isn’t this going a bit far?

Naturally, with a month until the iPad’s launch, nothing is set in stone—at least not to public knowledge. This speculation comes from Global Equities Research based on usability evidence about Bing, including the fact that instead of Google’s inverted triangle heat map, Bing has a rectangular heat map. Bing also uses layouts including several panes that are well-suited to rectangular screen.

Rectangular? Layout? Remind you of anyone? (The iPad. Also has a rectangular screen. But then, so does my computer and I still use Google.)

If this happens, the move may help Bing a little, but I doubt it’ll hurt Google in the long run—and since it has nothing to do with the Nexus One, it’s hard to imagine it’s going to hurt the competition in that arena.

What do you think? Will Apple really team up with Microsoft to spite Google, and if so, is it because of Bing’s usability results?