I have to correct my previous comment #5
There is no conflict between plymouth and psb_gfx but the problem is only 'vt.handoff=7' as kernel parameter..
This doesn't allow KMS to detect the correct resolution and employ the psb_gfx framebuffer as VT7, resulting in a black screen instead of X.
Anyway this should probably refer to a new bug report.
I believe that with the 'poulsbo' module fix above by Leann Ogasawara and with the blacklist of 'vt.handoff=7' the gma500 will work out of the box in Precise.