It’s looking like there will be some downtime for the Steam servers tomorrow (10/11).
Valve news says that from 4 to 8 am Pacific time they have some down time for…well…pretty much all Steam services. This includes the community, multi-player functionality, and downloading games. Hopefully you have a few offline games you’ve already downloaded.(So make sure you setup your account for offline play, otherwise you might be out of luck :p)