In applying for your applications to be in Microsoft's Windows phone market place or Xbox marketplace, you have to fulfill a few things, swear to a few things, and give a few drops of blood. But in addition to all that, you have to make sure that your software isn't licensed under, nor does it include GPLv3 software, code, or libraries.
Microsoft bans certain license types under an "Excluded license" provision stating:
“Excluded License” means any license requiring, as a condition of use, modification and/or distribution of the software subject to the license, that the software or other software combined and/or distributed with it be (i) disclosed or distributed in source code form; (ii) licensed for the purpose of making derivative works; or (iii) redistributable at no charge. Excluded Licenses include, but are not limited to the GPLv3 Licenses. For the purpose of this definition, “GPLv3 Licenses” means the GNU General Public License version 3, the GNU Affero General Public License version 3, the GNU Lesser General Public License version 3, and any equivalents to the foregoing.
I'm not sure why they limited it to GPLv3 here, as there are several GPL and other licenses which would apply, but I guess you have to start somewhere.
If you are building mobile apps for Windows Phones, steer clear of pretty much any GPL documentation, code, or libraries. Additionally, don't license your own app or code under either of them in hopes of community participation or PR buzz. BSD license would be fine for instance.