So – I just bought the new game Supreme Commander 2. This question is not about the game, but about the online software installation platform that it seems to require. I haven't bought a game in a long time, and I'm puzzled: Apparently, SC2 is a "Steam"-powered game.

When I went to install the game, it asked me to either create a new Steam account, or log in with an existing account. I clicked "Cancel" because I don't plan to play online and I don't want anything unnecessary installed on my computer, since I only plan to play single player!

However, after clicking "Cancel", the installer asked for my confirmation that I indeed wanted to cancel installation of the game! I thought I was just canceling the "online" portions!

So I really want to know:

• How do "Steam" powered games work?
• Is this essentially a form of DRM (Digital Rights Management)?
• Can I trust this software platform?
• Has anybody done any independent verification on how this platform works? (I'm very leery of any DRM after the Sony BMG CD copy protection scandal. Thank goodness for Mark Russinovich.)
• Does the "Steam" platform install anything particularly nasty or unwanted on my computer?
  

Imagine if the software in question were a productivity application. The issues remain the same.