It's frustratingly difficult to immediately work on the "unknown filesystem jffs2" problem because more often than not, the same kernel for me fails to even reach that stage (see my "another boot hang" thread).
Switching to Deepak's 2.6.30-rc5 kernel for XO, both problems mysteriously go away. Here are the files and the procedure if anyone else wants to try it out.
http://dev.laptop.org/~dsd/20090604/
I don't know what else works or fails in Deepak's kernel, or if there are any plans to ship it instead of the Fedora kernel for these XO-1 efforts.
What about the 2.6.30-rc8 kernel that's sitting in koji waiting for the F-12 rawhide floodgates to open. You can get it directly from koji here http://koji.fedoraproject.org/koji/buildinfo?buildID=104641
Peter