I second MegF's response.
I don't mind pushing a button for a little extra $$, so long as I am 100% NOT responsible for dimmer check/speaker check, replacing blown lamps, etc. AND that I get time with one of the electricians to show me how to trouble-shoot for problems mid-show, how to shut down at night, etc.
I ran into issues the last time I did this because the theater's ME was basically a huge jerk. And even though the PM had assured me that I would get a tutorial from him before I ran the board for the first time, first dress rolled around and the ME acted like that was the most absurd thing he had ever heard of and essentially told me that I didn't need to know anything except where the GO button was. Long story short, I got a tutorial from the electrics intern while the ME was at dinner. Then, halfway through the run, he changed the board. I walked into the booth one day, two hours before curtain, and had a completely different light board with different sliders, different buttons, etc. No warning, no note, nothing. I had... some heated words with the PM about that one, and got another tutorial from the very helpful and apologetic electrics intern.
So basically what I'm saying is, whatever concerns you have, voice them before you agree to do it. And whatever you agree to, get it in writing and HOLD THEM TO IT. Don't do anything you're not comfortable with.