Yesterday Google CEO Eric Schmidt joined Apple's board of directors. As several folks have pointed out, the appointment is ostensibly bad news for Microsoft, which faces the prospect of two of its biggest competitors collaborating on the direction of both desktop and online media. I think this is true, but I would add that Google's Schmidt will benefit from closer ties to the entertainment industry, and now has an "in" at Disney for video distribution.
Apple does several things well that Google could benefit from, up to and including the OS. There's also Apple's expertise with GUIs and their success selling songs and videos through iTunes (against which Google is an indirect competitor). It will be interesting to see if AdSense infiltrates iTunes. It will also be interesting to see if Google starts working more closely with Disney. As you may recall, Apple's CEO Steve Jobs is on the Disney board, after Disney acquired Pixar in January. (FWIW, Disney's ABC was the first network to distribute its shows through iTunes.)
As for Microsoft, Schmidt's appointment probably means Redmond will become even more disentangled from Apple. Google could show up in everything from the iPod to an Apple iTunes cell phone.
Also: Niall Kenedy shows how the board members were already pals. If you look at their bios, you'll notice each has a role in developing Web-based strategies, from Quicken to Current TV.