Lots of plusses and minuses, but like a previous respondent, I'll cover some of the negatives since plenty was said about the positives. I ended up nursing our now 12-year-old son for the first year of his life. It was well worth it but it was bumpy at the start.
I thought I'd love nursing (which I eventually did), but for the first month or two, I kept saying, "They SAY I'll learn to love this and it will be worth it...." But in the beginning, I wasn't so sure. It was all-consuming.
My nipples were raw (my sister joked that she used her breathing techniques for nursing more than for the birth itself); I had mastitis periodically (infection of the milk ducts); my breasts were the size of large grapefruit or bigger; if I was late for a feeding, I leaked all over the front of my clothing if I wasn't properly prepared; sometimes I just didn't want to be needed as often as I was needed (did I just say that?!) and I just wanted some extended time that was just for myself. Plus, it wasn't always totally intuitive to me and I felt inadequate when people would say "I just LOVED nursing." Is that enough of a rant? Oh, wait, one more...I had an emergency C-section so I was also recovering from the surgery which made it hard to sit up and hold my precious little bundle.
That being said, I also learned lots of tricks to help with those problems.
SORE NIPPLES
My nipples were raw, cracked, bleeding, etc. in the beginning...our son was a voracious nurser right from the start. My sister later said it helps to gently rub your nipples with a washcloth before your baby is born so that they get used to more activity. (NOTE: I still remember when our son was first brought into me to nurse. I said "Hello, little one." and he turned his head to figure out where that familiar voice was coming from! : D )
Had I known what I was getting into, I think I might have bought the double-breast pump earlier and expressed milk right from the start to give my nipples a break on occasion.
MASTITIS
Warm baths and showers help a LOT to soothe the pain. Manually expressing milk during your shower can help clear out the ducts and infection. But it's kind of funny squirting breast milk during your shower. Nothing like adding to the entertainment of life.
GRAPEFRUITS
I guess that's an individual thing. I swear they almost doubled in size! I was known for producing very rich, profuse amounts of milk at the daycare. We joked that I should sell it in bulk! I'm sure there could have been a market for it!
LEAKAGE
I bought a ton of nursing pads--cotton lined to absorb, waterproof material on the other side to protect my clothes. (Skip the disposable ones. Too expensive in the long run and not always as absorbant.) And not all washable nursing pads are equal. The slightly contoured ones worked the best for me. I could wash my pads to my heart's delight and have them at the ready any time I needed them. They were a godsend! Sometimes they leaked, if I was flowing too freely, but in general they worked like a charm.
NOT WANTING TO BE NEEDED THAT MUCH
You have to remember this was our first and ultimately our only child. I just wanted uninterrupted sleep, to finish a project, or to read a book without interruption, and...did I mention sleep? You're already aware of what being a parent does to your free time, so that may not be an issue for you. : )
At about 6-8 weeks or so, I started pumping with a breast pump so that I could save some milk for my husband to do some night feedings. He was a saint! He always woke up much better at night than I did. (And we had our secret weapon...Mr. Clock...a old-fashioned wind-up clock that did wonders for putting our son back to sleep.)
I quickly learned that a single pump was not going to work. I'd start pumping one side and the other side would start flowing. I eventually bought a Medela Pump-in-Style breast pump. It is a double pump so you can express milk from both breasts at the same time. Those things were brilliant!
Sometimes I had to chuckle because I kept imagining the sound of milking machines in a cow barn. To this day, I remember the sound of the pump. But it was totally worth it. And your health insurance, if you have it, may kick in for some of the cost. The pump is not exactly inexpensive but it is TOTALLY worth it!
The pump helped me to get a break on occasion or to go out on an errand on my own (gasp!), knowing our son had lots of yummy mommy's milk at the ready. Plus, it gave my husband a chance to bond wonderfully with our son as well. It even gave me a rest if I had plugged ducts and I could feed him with the bottle. And it helped when my breasts were ready to bust but our son was sleeping.
FEELING INADEQUATE
I truly came to love nursing and found it easier and cheaper than formula, but you couldn't have convinced me of that in the beginning.
We smile about it now, but my husband and I actually got into arguments about the "right" way to nurse--what angle was best, was our son getting enough milk, too much milk, etc.? What classic first-timers we were!
When I would be somewhere other than home, it felt like such a production, when pulling out a bottle seemed so much easier. However, I learned through time that it really was easier--no clean water source to find, no storage issues, just stop the car and nurse, then merrily continue on your way. (But I was never one of these people who could go without a bra. Small-breasted women could probably skip the bra, making the nursing thing a lot easier--no unhooking and rehooking the bra to contend with.)
C-SECTION
When I first started nursing, I was still recovering from my c-section. It was hard to sit up without discomfort, it was hard to switch positions without pain. Call me a wimp, but I'm lucky I had help in the beginning for setting up pillows, etc. Eventually, we figured out a system that worked well. I would sit in my husband's grandfather's old leather chair. It rocked and was big enough to handle a bed pillow on my lap with our son on top of that. We could both then relax in comfort as our son nursed. Ahhhhh...
DISCRETION
I didn't mention this above, but the decision also depends on how comfortable you are with the idea of nursing. I was totally comfortable with nursing, but my in-laws felt really weird about it. We struck up a compromise. I would put a soft blanket over my shoulder so that they felt comfortable still being in the room. Our son could nurse but it was discreet enough for their comfort zone. Personally, I think it was kind of a cozy little spot for our son!
So, there you have it. A bunch of cons, but also ways to get around them to make it a better experience. Good luck deciding! Regardless of your decision, enjoy your bigger family this fall.
P.S. Not everyone can breastfeed. A friend's baby wasn't getting enough nutrition from her milk and needed to go to formula. But you'll find out if and when you get there.