Endorphin release and receptors aside, an addiction is any which activity which impairs your ability to function normally should you:

a) continue doing it.
b) cease to do it.

By that definition of course we're addicted to breathing and eating, but it's a fairly valid acid test.

For example, I'm addicted to caffeine. As long as I have 3/4 mugs a day I'm fine, but if I stop I get a killer headache which impairs my ability to function.

If you're masturbating 15 times a day, I'd imagine that would classify as an addiction because (unless you're Flash) I imagine that would mean that you're skiving off work to run and have a tug.

Addiction is just another illness though, if you're happy in your addiction and it doesn't hurt anyone else then I figure: go forth! I'm sure as hell not giving up the java.