I read somewhere about using an adsense ad in emails to mailing lists, is this possible/allowed or a future expansion possibility just like the beta tests for RSS feeds they did?
I believe it is limited to very specific high volume publishers. It is not something accessible to your average member.
I never heard anything about it and I dont think they are ever going to allow this. for now...no never put your adsense code in any eMail...its clearly against the TOS.