Hey guys.  
 
I just got a new rig (Mac Notebook Dualboot -> proper gaming pc). Since I have games and only games on the Windows installation I did not really bothered with backups. So I do need to download everything fresh on the new computer. Is there a "button" to hit that just downloads and installs everything (also I am moving from 100GB -> 1TB, so finally enough space for everything), so I can start that and got to work and play my games in the evening?

Steam will download the games you have bought, but you would be limited by your net connection.

 @mosdl: I think he is asking if there is a way to cue every game he bought to download while he is gone one after the other. 
Unless he want's to download all at the same time.

just click on what it is u are going to download and download it. it would take you all of 2 minutes to que up everything you want. then yes all of it will download.. but there is not a button that just downloads everything you own to my knowledge.

steam should do what itunes does and have a button for turning on simultaneous downloads on or off

Just click Install on all your games in the Library tab and go to work. When you come home your games will be ready.