I'll join the boat that's got "portion control" written on the side. I personally believe life should be enjoyed and that you shouldn't restrict yourself the pleasures of dining out. Yes it's terrible for your health most of the time, but if it's a once in a while event then why not?
I think the key to being "good" at a restaurant is SLOWING DOWN! Man, I am so guilty of being presented with a heap of food and inhaling it! I read a book called "The Japan Diet" and a section was on the way you eat to help with weight loss. Take a bite. Put down your fork/spoon/chopsticks/spork. Chew. Reeeeallly chew. Swallow. Pause. Take a sip of water. Talk a little. Continue. Seriously, it takes a lot of self control to do it but you will find yourself filling up a scary amount faster than you realised. Most importantly STOP when you feel full! Then just throw away what's left, don't take it home! A waste of money, perhaps, but that's the price you pay for indulgence!