If it IS patented
...then in a naive interpretation of patent rules, Google can't put it in without getting a licence or getting a lawsuit. And the same would apply to some hacker adding the feature afterwards, if they're within reach of U.S. law - and nowadays that reach is surprisingly long. They'd start with a cease-and-desist letter and maybe finish with the guy in jail. I expect that multitouch function is useful to terrorists as well as anyone else.
In a less naive interpretation, doing something you -could- be sued over isn't always bad business, and, leaving aside the justice or injustice of software patents, anything you make a computer do probably breaches someone's patent. You just hope they breached someone else's and you get what I think is called a Mexican Stand-Off.
As for trademark, if it -is- a trademark, I don't think "multi-touch" is a common phrase since time immemorial, but on the other hand it's been bandied around for Windows 7 and Microsoft Surface without comment, so I'll presume that was a mistake.