warpig - one bit of advice I will give you, all the books say breast feeding is easy and painless - it's not, it can be toe curling agony. BUT , if you do have problems, stick it out for 10 days and after that I promise it will be fine. And if you have problems getting him/her to latch ask for help.
I'm not obsessive about breast feeding as I know it's not right for some people, however I loved breast feeding my son and when I went back to work I expressed milk even though I didn't seem to have loads (I would only feed him on one side during the night and express the unused one in the morning) my baby thrived and he never had a drop of formula. Everytime I got in from work it was like rebonding with him all over again!
Best of all I didn't have to spend hours preparing formula, warming it up, sterilising bottles, getting bottles ready everytime I wanted to go anywhere - So we could just grab a nappy and go anywhere we liked, whenever we liked. Also it's much easier in the night to grab your baby latch him/her on and snuggle back under the duvet until he/she's finished than getting up and warming a bottle in a cold kitchen.
If you want to go out for the evening just express.
Good luck!