Just to wrap-up the threaed and give feedback:

- when my friend arrived from Canada, the custom in France didn't stamp the passport. We noticed it once we'd left the airport. Then we went back to avoid further questions when going to Switzerland. Customs apologized they forgot, confirmed it is necessary at the entry and stamped the passport without further questions.

- on the way back, living Switzerland, no stamp as well! In GVA, custom said it will be stamped in Franckfurt (connection there and place where living Schengen). Then in Franckfurt, my friend had to asked for the stamp - they didn't do it straight.

Conclusion: is it still so mandatory to have passport stamped ?? If not, how control of stays lenght is made ?

Thks,
R