[torstenvl]

I don't think that's quite accurate either. Although you can include MIT-licensed code in a project that is, as a whole, licensed under the GPL, you still must include the original license and copyright, rather than "going from MIT to GPL."

For example, if you have an MIT-licensed project and I contribute to it, my MIT-licensed contribution will remain MIT-licensed, regardless of what you do in the future. If you change your project license to GPLv3, and later can prove that someone used my code from your project after downloading your project's source, I do not think you will be able to successfully hold them to the GPLv3 and force them to release the source of their derivative work.