If only it were that easy. I work at a school of 600+ students as the sole IT person and we went with Google Apps 2 years ago and it was probably the single best decision I ever made. The amount of work and stress not hosting an in-house e-mail server relieved was enormous. If you can have people dedicated just to the server stuff, ya, I see your point. But not every organization has the luxury of employing enough IT staff to adequately run all services in-house.

No, they still cannot access porn.com with a good web filter. Yes, the search may not necessarily be filtered for porn.com, but once they click on the website, the normal web filter will come back into play and the student will be blocked.