Okay to play more than 1 game simultaneously on Steam?

[meths]

As title really.

I've got two monitors and sometimes want to have two steam games running full screen at the same time e.g. if i'm mining on Eve and want to play a bit of Plants v Zombies while I'm waiting on my ship to fill up.

Will this cause any problems with my account?

 

[meths]

You can do it but I was just wondering whether it's against the terms of use and could result in your account being banned.

I'm at work just now so I can't check on the Steam site.