Although the percentage of you who want to customize the Tiles on your Windows Phone is pretty small (not to mention technical limitations like being developer unlocked) the project by Windows Phone Hacker has had some success and interest. An update is in the works and it looks to be quite good for those who are into this scene.
We originally saw the Themes homebrew app released last December and now Jaxbot is looking to update the program with some new features and a redesign. The new version will allow you to download themes right from a server negating the need to sync them from your PC. In addition, the UI is much more streamlined and it's easier to add Tiles. The downside is you still need to redeploy tile by tile and Live Tiles don’t work (though Jaxbot notes that an SMS tile notification is possible).
No word on a release but it looks like the project is quite far along, so it shouldn’t be too long. Head over to Windows Phone Hacker and let Jaxbot know your thoughts on the project. And remember, you can always head to our forums for more custom themes.