Thanks for reporting! Now it was different and the face tags has disappeared for both Picasa and MS tags. The error now came from a code sharing between Photoblogger and Tiger, but the former has handled the global "use regions" switch a bit differently.
I just noticed as well that my face regions exported from Adobe Lightroom no longer appear in the lightbox. The region metadata is there in data1.json and the regions are displayed in jAlbum's region editor. I backtracked through previous versions of Tiger that I had on hand to see when it might have broken. I can say that the regions display fine in Tiger 2.6.2 and do not display in v2.7.1. So something broke between those versions. For now, I am reverting to 2.6.2 and rebuilding all my albums.