I never do weights and cardio on the same day, ever. I tried it for about a month and didn't like it. I don't even wear the same clothes/shoes/etc. FWIW, I do cardio three or four days a week and weights twice. Of course, I am just a gym rat and not an expert on any of this.
This site is kind of cool, although I've only skimmed it.
Also, RU OX, do you ever do intervals? I would recommend that (although again, I'm not an expert -- it just makes sense to me).