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.
They definitely aren't pioneers at this. Steam (a game store) has been doing this for over 5 years, and started offering Mac games as well about 8 months ago.
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.
That's fine for Apple software, but you can bet that 3rd parties aren't going to be chomping at the bit to give Apple an extra cut of their profits just to prop up this new app store. It may be a boon for indie devs, but that hardly means it's going to revolutionize anything. Microsoft and Adobe are both absent at this time, so no Office or Photoshop. I'm sure there are plenty of other examples, but you get the point.
Besides, last I checked there is no easy way to re-download anything you buy on iTunes or the iOS app store, so why would the Mac app store be any different? The previous example i used - Steam - is far superior in this regard. I can download any of the games I've purchased any time, as many times as I want, on any computer anywhere.
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.
Their offerings are plenty robust for a Linux distro. You'd probably find them lacking if you were expecting to download a bunch of AAA software with them though. But the same is true of the Mac app store, so I'm not quite sure I see the relevance. Big software companies prefer to control their own distribution. You said no one has tried it before, I'm just point out that that's incorrect.