Well, I travel a bit in the region and found this great place in Nairobi called Milimani Backpackers. I was at the old place where they no longer are, but the new place takes this backpackers spot really to new heights. Serious, the guys are friendly and help you out a lot. They listen to problems and you will not find super quality with such great price as here. They moved now to Dennis Pritt Road, at the very end of it....totally green and quiet environment with a pool and sunbathing area...basically the best place to relax when you are going for safari or if you are on your way back home. The place is cleen and the food is great as well. Glad to have been with you guys!!!!!!!!!! Scooby (the dog) is the best;-)

I had not been to Nairobi before and so I don't know how it compares to the other hostels but this was very basic. I paid extra for an outside single room however it was very noisy from the hotel next door. It probably would of been quieter inside in the shared rooms.
The staff were extremely friendly and knowledgable and the bar area was a great little place to sit and meet other travellers.
The food was basic and cheap - 50ksh for a cup of tea, 180ksh for a beer. Not too bad at all!

I can't comment on the distance to the city but it's well known with the taxi companies and around 2400ksh to the airport which wasn't too bad split between 3 of us

A decent place for one or two nights. Don't expect luxury, or decent bedding but it's not bad

This place does the bear minimum in serving their guests but they do the maximum in trying to scam every dollar out of them. The facilities are terrible and the price is high. Everything costs alot here. The place was dirty and broken. My bed had definitely been slept in there were obvious stains, hairs and skin in the sheets. I could barely get the surly staff to replace them. I did not feel welcomed or respected whatsoever.

The backpackers can be easily reached with public transport from the bus / train stations in town. Nairobi's public bus system in general is quite good (and a lot cheaper than haggling with the cab drivers for a fair fare).
We stayed before and after a group of American missionaries had booked the whole place and therefore got to test two different dorms.
The dorms were clean and with enough space. Please note that there is a cheap cheap dorm in a tent which I didn't get to test but heard horrendous things about. Apart from the dorms there are also doubles.
One of the dorms I stayed at came with en suite facilities. Both the en suite and the shared bathrooms were clean and with hot water but the showers in the shared one are a bit inconvenient: there is no private space apart from the shower itself so that you have to show some artistic skills to get dressed in clean clothes without exposing yourself to fellow guests.
There is a bar / restaurant with a wide range of drinks and dishes and a cozy fireplace. Prices are ok. But if you're on a budget budget go to the eatery / market place behind the backpackers (leave backpackers, turn left, left again and up the little alleyway).
WiFi and computers with internet are available against a charge (200KSH per day). Wifi only works in the common areas and - if you're lucky - the first dorm on the left (aka the girls' dorm).
The backpackers has a travel desk where you can book all sorts of tours to popular Kenyan tourist destinations. I didn't try them but the ladies seemed to be quite capable.