Man, some of the posters here make it seem like there is no point to keeping a family whole... As many have said, it really depends on the particular situation that you are going through. I'm a child of divorced parents. It was painful. Stepfather was also gone after about 13 years. There is no way having divorced parents (no matter how civil) is EVER better than having both loving parents in the same household.
I think as a society, many of us (not all situations are the same, of course) see divorce as something more the norm than being married to the same person your whole life. Many people go into marriage not thinking this is a lifetime commitment (evident by the rise in pre-nuptial agreements). Marriage is HARD. It definitely has its up and downs. You might think that your partner has changed, does things that annoy you, etc. From our own point of view, we are always right; but we have also changed through the years and we most likely also do things that drive our spouse crazy.
I resent my parents to this day because I never felt they made a concerted effort to compromise and work on their marriage. They are both very selfish people and it shows in everything they do to this day. I love them because they are my parents, but I have learned what not do do from watching their relationships and hope I am a better father and husband.
As someone else already mentioned. Unless there is something that happened that makes you feel it is irreparable (infidelity, etc), you don't want to feel that you left without trying everything, if both of you are wholeheartedly feeling like you want to give it a shot. You also have to agree not to badmouth, make derogatory comments, etc in front of your daughter (my parents were horrible at this and made us part of all their arguments - sucked). If possible, forgive, forget, and start new. Once you've exhausted all resources, you'll have the answer you need to make your decision. Once you've felt you've done everything you could, you will not ask us for advice. You will have no doubts about the decision you've made.