I tandem nursed my sons for about 3 months after the birth of my second. It was a very special time for us, but also challenging for me. DS1 was a terrible nurser - frequent but always very painful. I had a hard time putting up with the pain during the pregnancy but knew that he really needed that from me and had wanted to let him self wean. Once DS2 was born, I realized how wonderful and pain free nursing could be! It was very hard for me to either go from one good nurser to a painful one or to balance the pain when they nursed together. Thankfully, DS1 very much accepted weaning after a few months.
This time, I don't have much pain and I am looking forward to whatever happens. DS2 is only 15 months so I really hope that he will continue nursing until after the baby is born - I can't imagine having him wean before 2 yrs. Oh, the other big difference is that DS2 night weaned recently, so I might actually be better rested (hoary!!) this pregnancy. I had forgotten what it was like to sleep through the night without someone wanting to nurse every hour or two (its been over 4 years since I last slept the whole night through)