Tom - I was recently lucky enough to have someone (the fiance!) buy me (most of) a D3, the downside was I had to give her my D300 - a fair trade no doubt as the D300 has been a great camera.
I have a deal with her that should I ever need to use 2 bodies that I can borrow the D300 anytime - so I think I ended up with a win-win deal really.
I was suffering from the same problem - but I've made a pact with myself, to at the very least take 1 photo a day - so far it's going well.Like you, I've got a D300 kit but I'm struggling to find the time to make good use of it due to work and other hobbies that consume much of my time.
Thanks again.