Definitely check out kellymom.com recommended by badgergirl, but there's lots of data on the hormonal impact of night feeding. We deliberately co-slept with our 2nd after supply issues with our 1st and it made a huge difference. However, I started pushing night weaning at 15-18 mos. DD could understand that mama's breasts "needed to sleep" to make more milk for the morning. It went much faster than I expected. Sometimes a little nudge is easier than you think.
CW-125, part calorie counting, part transition to primal
GW- Goals are no longer weight-related