As described in summary and discussed with Ray on IRC, booting 20091009 x86_64 desktop live image gives the plymouth text boot - the text progress bar, with KMS enabled - rather than proper graphical boot. Test system has a Radeon HD 4770 graphics chipset. Will test on an NVIDIA 9400 chipset soon. lsinitrd shows the relevant kernel modules _are_ in the initrd.
update: works OK on intel (tested by Ray) and nouveau (tested by me), but confirmed to fail on another radeon system (by Ray). this is radeon-specific but affects multiple radeons (probably all). -- Fedora Bugzappers volunteer triage team https://fedoraproject.org/wiki/BugZappers
misdiagnosis: actually works with dual-head, but fails with single. ray is working on a fix. -- Fedora Bugzappers volunteer triage team https://fedoraproject.org/wiki/BugZappers
fix is building now.
Tagged earlier.