Many distributions of Linux have been doing it for years. And it's hardly a new concept even in the Mac-o-sphere, they just ported the idea from their phone. Honestly I don't think it's going to catch on. It worked on phones because there was little to no existing infrastructure for selling or distributing mobile software, but major computer software vendors aren't going to just bow down to Apple's whims.
I do, it takes the time out of looking for software on the web and removes waiting for cds. I've downloaded a bunch of programs, but, unless I know they are recoverable if my comuter has to be reformatted, I am hesitant to not get a cd, the app store removes that. I wasn't going to bother updating iphoto because I didn't want to either go out and buy a cd or order it online and wait for one. Linux may do it, but with the market share not only of linux, but of the particular distributions that do it, I wonder how robust the offering were.