There is no inbuilt option available in Lightroom to import from Picasa to Lightroom.
However, you can try and follow the below link to import face recognition information from Picasa to Lightroom.
Please let us know if this helps.
I don't believe Friedl's plugin will import the tagged rectangular regions identifying the location of each face within a photo. I think it just imports the list of people names assigned within Picasa into LR, converting the names into LR keywords.
To import the rectangular face regions as well as the associated people tags, see these two threads for hints on how to do this: