PSA: Don't count on this to be secure. Not just because Koding can obviously monitor everything you do, but because the implementation appears to rely on some more or less flimsy kernel container isolation (user namespaces etc). This means hackers can break out of one instance of this and enter others. So please, don't use this as a bouncing point to SSH to other servers or for anything else that might be even a little sensitive.
Also, it's apparently unpatched since May:
$ cat /proc/version
Linux version 3.9.0-0-generic (root@salt-master.in.koding.com) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #4userns5 SMP Mon May 13 06:15:34 PDT 2013
I have $1000 here waiting for you if you can break from one container to another. I need valid proof in the form of source code for your exploit. send it to hello @ koding.com and we will paypal you the money.
Also, it's apparently unpatched since May: