ShareAlike means they're unusable for commercial applications. I suppose you can still use them on a website, but I'm not sure how much of the website you'd also have to make CC-BY-SA.

Their FAQ implies a more liberal license, though:

http://subtlepatterns.com/about/

No, ShareAlike means you have to distribute them under the same licence. Unless there is a NoCommercial, that doesn't mean you can't sell them, you just aren't allowed to change to a more restrictive licence. IANAL.