^^ She made the statement in 79's long oil consumption thread. She said that her dealership recommends against Mobil1, and will only use it if a customer provides it and specifically requests its use. She says that she's seen engine damage from customers who use Mobil1, but her evidence is circumstantial as there can be many causes for engine damage.
Regardless, she's a service writer at a Subie dealership, and has seen lots of Subie cars come through her dealership's shop. If she sees a pattern, I may wonder about its validity, but I'm not going to risk it to save $7.50/oil change. My car isn't burning any oil right now (at 8k miles), so I'm happy with how my Impreza is running with the Amsoil.
If it ain't broke, don't fix it. Right?