rudeguy - If they treat you as a temp worker, and you get no benefits/OT, then you put in your 40. The work will still be there tomorrow. Don't work extra because you feel obligated to. Good impression? Sure, but you also show you are a pushover. Believe me, they notice, and will take advantage of it if you offer it up.
Others have said they've shown their true colors, which may be true, but at the end of the day, they are in it to make a $$. The longer they keep you as temp, the better off for them.
If you like where you are at and want to continue, then go talk to the CEO. Put together a presentation of your accomplishments and say you want to be hired and here are the reasons/what you've accomplished there so far.
At the end of the day, if you are as integral as you say you are, then they need you as much as you need them. There's a chance this could backfire, but at the end of the day, respect for yourself > just having a temp job.
Good luck RG.