Lightroom plugin which extract picasa face information from XMP-mwg-rs metadata and convert it to XMP-MP microsoft standart metadata, write names to "PersonInImage", "RegionPersonDisplayName" tags and also create lightoom keywords for every poeple on the photos.
To use plugin check in picasa "store name tags in photo" is checked, label all faces, select this photos in Lightroom and choose "Library/Plug-in extras/Write Picasa Faces to Tags" after that save metadata manualy Ctrl+S.