Just a quick note, I have had a 7805 ACT? (100mA version) connected to a 9V Battery for over 2 years now, the PIC controls a CCTV Camera (Pan, Tilt, Zoom) Pelco D protocol, and although constant use isn't there, it is used a tool for camera engineers on site work visits fairly reguarly, and it is still going strong, it is a Duracell Battery.
I was quite surprised when I switched it on the other day and it still worked perfectly.
So for low current applications, that little regulator is very good in my experience.