A little trick I figured out was to take a short 1" piece of black electrical tape and place it over your rim's valve hole on the inside of the rim the next time you change a tube. Smooth it on good over the hole, then take a sharp pen or an awl and poke a hole in it so the tube valve can go in.
What this does is cover the sharp edges of your metal rim hole with smooth tape so that it is less likely for the tube to get cut if the valve gets wiggled or pulled on when pumping up (even though we all try our best to avoid this). Similar idea to your rim tape that covers the spoke holes and protects your tube.
Other people apparently file the edges of their valve hole to smooth it, but I'm lazy and the tape trick works for me. Anything that can help prevent a needlessly ruined tube is a good thing I figure.
Anyone who tapes up their own bars will have black electrical tape on hand.