Some people have used custom locales/custom cultures successfully and others are finding scenarios that don't work. Feel free to comment about what scenarios work/don't work for you. I'll try to update this when I learn about new scenarios.
Things that work:
Please let me know of any other cases that you run into, or any workarounds you find. We're working on some of the known limitations, but some of the issues are complex and will take some time until a full solution is available.