The question becomes really simple if you are releasing as free and open source and everything using your code is also free and open source: everything will be fine as long as your code is using a compatible license. If your code is proprietary or is used in proprietary software, it becomes a bit more complicated. The main question is whether or not you or others are using your MIT licensed code in a proprietary manner.

You can link to code covered by the [GPL even in proprietary systems as long as the license is compatible][1]. The MIT license is generally compatible with the GPL, but I recommend [asking FSF directly][2] as these [multi-license situations can be tricky][3].


[1]: http://www.gnu.org/licenses/gpl-faq.html#LinkingWithGPL
[2]: http://www.gnu.org/licenses/license-list.html#LicensingEmailAddress
[3]: http://www.gnu.org/licenses/gpl-faq.html#ManyDifferentLicenses