Recently stumbled over this blog post: http://labs.trolltech.com/blogs/2008/12/04/how-kde-4-is-blocking-qt-45/
Looks like it's usable for KDE 4 trunk already, and the improvements to the WebKit engine got me interested in trying it. So I spend 2 hours in creating ebuilds for the Qt 4.5 snapshots - based on the split Qt 4.4.2 ebuilds in portage.
That actually wasn't that hard to do, just fixing the qt4-build.eclass to include that 4.5.0_pre* version, and adding one line to qt-core ebuilds (adding src/tools/bootstrap to the targets). Other than that, it compiled fine. Easy.
The overlay can be found in my SVN:
svn co http://gimpel.ath.cx/svn/qt-snapshots
There is an update-qt-ebuilds.sh script in the Scripts/ subfolder, which should generate an updated headers tarball and update all ebuilds. Just adjust that distdir variable.
And now the usual warnings etc: USING THE EBUILDS IN THIS OVERLAY MIGHT KILL YOUR CAT, BURN YOUR HOUSE, BREAK YOUR CAR AND YOUR KDE4 and whatnot else. Use at your own risk!