GDC is currently developed by a very small group. While the addition of a D front-end to GCC represents a great step forward for D, it also represents an informal promise by the D community to keep the D frontend up to date with the latest GCC development.
Thanks to Github and Git, contributing to GDC is as easy as forking the repository and submitting a pull request (although this workflow will likely change when the merge is officially complete), and filing a bug report is a simple web form.
If you use GDC, we encourage you to try to contribute, whether by submitting bugfixes, new features, documentation updates, web page improvements, etc. In the past, GDC has nearly died due to poor communication and lack of development. Avoiding those issues is easier than ever before, but GDC will always need a community that's willing to give back.
If you are looking for a project to help improve GDC, check the project ideas page.
Work is currently under way to merge GDC into a future release of GCC. Any assitance of any sort during this time would be invaluably appreciated. Feel free to contact me via email or message me at #d.gdc on FreeNode.