As mentioned in this week's Gentoo Weekly Newsletter, the X team has now unmasked 289 modular X packages. They are now ~arch (testing) for most architectures. Be sure to read the migration guide before upgrading to modular X.
If you have any problems, the Modular X server bugs, annoyances and solutions (Part 1) and (Part 2) threads on the forums are the correct places to read and post any issues you have.
