Question for men 30+: In general, when do you make a commitment/want to become exclusive?

Do you make a commitment/become exclusive once you've fallen in love with a woman, or do you commit BEFORE you're in love with someone and focus on developing one relationship at a time?

Also, when single, how long do you think it's appropriate to "keep your options open" and date multiple people before you settle down with one and become exclusive (assuming that you ARE ultimately looking for a long term relationship, and not just looking to get laid)?