This is not a good change, yet!!
1 - it sets a VERY UGLY bold to the default fonts, on Mac/iPad/iPhone
2 - the option to use Open Sans as a remote font is not indicated in the ACP in any meaningful way
3 - the option to use Open Sans is tied to jQuery as well. If you want Open Sans, you must use jQuery via CDN. If you don't want to use jQuery via CDN, you must use the default fonts. There is no separation between these two totally different features. And none of this is described by the setting for CDN usage in the ACP either.
There should be separation between loading jQuery and loading Google fonts in the ACP settings.
Really should just find a nice font that looks the same across both platforms and that has a compatible license.
Discuss here too: http://area51.phpbb.com/phpBB/viewtopic.php?f=81&t=44735