I'm in the process of weaning my 11 mo DD for the same reason - going back to work in January. We were doing 4 feeds a day also. I dropped the 11am BF in mid-October. She didn't even notice. I offered her formula and a snack instead. For us, though, she refuses a bottle (has refused since 4 months), so I give it to her with a straw (she can use a sippy, but just takes small amounts). She still only takes 2 ounces at a time, though. I dropped the 4pm BF 10 days ago - same thing, she didn't even notice, and I offer her a drink and snack. She's now BFing twice a day (though she's often refusing one side at night, and morning BF is really quick), and taking about 8 oz formula during the day (about 2 oz with each snack, and an ounce with bkft, lunch and dinner, and another 2 ounces mixed in with cereal, soup or other food). So, its gone smoothly, but I wish I could get her to drink more formula since 8oz a day (of which only about 5 or 6 is in liquid form, the rest mixed into food) isn't enough for when I try to drop the am and pm BF's (which I'm not planning to do for a while, but seeing DD is showing less interest, it might be sooner than I would hope).
Nic