I've already posted this in the Bridge forum, but I thought it might just be relevant to ACR too, so here goes...
I've just bought a Panasonic GF2. ACR support was introduced with 6.3, so I have no problems with opening its raw files in 6.3 or 6.4RC.
If I click on a newly-uploaded raw thumbnail in Bridge, a high quality preview is generated, as expected. However, if I select the entire folder, and select 'Build and Export Cache', nothing happens - I am returned to Bridge as if nothing happened, and the thumbnails stay showing the embedded versions.
This is something I do regularly with my Nikon D300 raw files. Bridge usually counts through the images, and the previews are updated with the ACR-generated HQ versions. But no so with the new GF2.
I wondered if this had anything to do with GF2 support in ACR, rather than Bridge itself?