As you might have realized, we are currently only showing the 2 default user icons on the server, Steve and Alex (the blonde one). This is due to the issue that the minecraft server providing these is frequently down recently.
We do not request these live from Mojang but rather request them periodically in a batch from them and store them locally. I have to wait until the server is back up and then re-request the icons. You can check their status updates here: https://twitter.com/MojangStatus
[Update] The servers work again and I now enabled a daily request of the icons.