Hi Tatopitta,
Well, it depends. I think that digital certificates are good assuming you want to buy them and send them to people. For some people that's expensive. I think for intranet, it's also not an IT policy to install certificates unless they are issued from the company, but I totally agree that digital certificates are the future.
For now, to simplify your life, if you do not need "auto-upgrade" support - in other words, if you don't need to have the users automatically upgrade the form when it changes - then why not use the regform tool and ship down MSIs to the client. That doesn't require a digicert.
But, why save a CSV file locally? Why not submit as an attachment to a website and e-mail them a link? That doesn't require full trust. I think the times when you really truly need Full Trust are few and far between. You're better off with domain trust.
Ciao!
Patrick Halstead [InfoPath MVP]
InfoPathDev
Patrick Halstead
Project Manager at Qdabra