GMiller--You will probably love WNS and the Nairobi area in general. Good luck on your fundraising--that is the only reason we are in the US and not there. You can PM me and I can get you in touch with several teachers who are there right now. You will have tons of fun at PFO in July, it is exhausting but you will form a great understanding of TCKs and build relationships with your team and others who will teach internationally.
To both posters, you are in very different boats, though. Mother of 2 boys, your place is listed as DC and your husband just got transferred, so I'm making the assumption he does some kind of higher level state job (if I'm wrong, I'm sorry.) You will probably enroll your kids at ISK, a FANTASTIC school. (With luck, I'll see you there in August...fingers crossed and prayers going up.) West Nairobi is also a good one, but it is Christian. If you are Christian and are okay with that, WNS is an excellent choice, with highly committed teachers and great facilities. Your financial situation will be very different. I imagine you will be able to afford a very nice house in the better parts of Nai, will likely have full time househelp, adequate water reserves and a generator for when the power goes out...and it will! The power does get "rationed" as does water, but since the rains have been a bit better lately you should have more consistent service than say, two years ago in the midst of a long standing drought.
GMiller, you need to pray for lots of generous donors. I don't know how many kids you have, but if Les hasn't already told you, you'll need about 2000-2500 USD in support a month, outside of the stipend, less if you have only one or two kids. That will get you a decent house, fairly close to school, someone to come in a once a week or so and clean, help with laundry, iron, etc. (You will need to iron if you line dry, take my word on it.) Cars are very expensive in Nai, since everything is imported. Expect to pay about 30-45% more than for the same thing here, or the equivalent, since there are lots of Japanese models that we don't really have here. Gas "petrol" is also much more expensive, last time I checked the equivalent of $5+/gal. It is sold in litres.
Some of the good things are the ready abundance of fresh fruits and veggies and "clean" meat. Almost all processed food is comparatively expensive, and you will pay upwards of $7 a box for "American" cereal, if that's your thing. As a family of five, we budgeted $500/mo for groceries, and we avoid most processed food. We got our numbers from friends there with similar family sizes. There is always something to do, whether it's Nairobi National Park--lions just outside city limits? Of course! There is the giraffe reserve, a place with monkeys that I can't remember the name for, Village Market with an awesome waterslide that I have only seen in pictures, health clubs, and more. Great wildlife reserves and national parks an hour or two from the city--Hell's Gate and Lake Nakuru, Lake Naivasha. Visit Nyeri and straddle the equator. Drive or take a short flight to Mombasa and enjoy the beach life for a holiday. You won't be bored, I promise.
I can't say enough good about the people of Kenya, since after all, I did marry one! :) Very friendly overall, many speak English, and Swahili isn't too hard to pick up. However, if you stay in mainly the "white" part of the city, you won't experience much of that. You need to take care and be reasonable, like in any large city of a few million. Be aware that next Dec there are elections, and you will need to be careful. The last elections were very bad and almost started a civil war. If possible, it would not be a bad idea to be in States for Christmas 2011 and New Years as a precaution. As for me, I haven't actually been there since 2000, but we were prepared to move at this time last year (ie, boxes packed and ready to ship nonessentials.) I won't get into details in that experience, but I think most of my information is pretty up to date. I love Kenya, Nairobi, and hope to be there at about the same time you both will, if it's in the Plan. Right now, I just dream from afar!