I stayed for one night at the YMCA Nairobi after flying in on a Friday night. I desperately needed to get in touch with a friend, and was relying on the internet, as I had no phone yet, but their internet was down (and continued to be for the length of my stay). However the staff was helpful and eventually I got in touch with my friend and told him I arrived safely.
I got a single with a shared bathroom for 1500 Ksh. The toilets were pretty disgusting; the light didn't work and the toilet didn't flush, but the shower rooms were nicer (at least the light worked) with good pressure and delightfully hot water.
Breakfast was good - but anytime I eat anything other than bread and blueband for breakfast I get excited, so my standards may be low. Anyway, it was cold cereal or porridge, lots of fruit, tea, eggs and sausages. The fruit was fresh and delicious.
For the price, it was a good stay, but I can't help but think there would be better places to stay in Nairobi.