I like how the newly downloaded builds auto-install on next launch of the application (ala Firefox). However, I think it needs to ask you to confirm before it does this with something simple like "MC wants to update itself to version 16.0.xx. Would you like to continue?" Then, if the user skips it, it should probably not auto-update itself in this manner anymore for that particular build (until the next one comes out). It could simply make a shortcut to the build's installer on the desktop, and then educate the user "Auto-updating for this build has been cancelled. Use the link to the installer here to initiate this update manually" (or something to that effect). There are three basic reasons I'm suggesting this:
1. Last night, I sat down at the HTPC to watch a show with my wife. MC was closed. I hit the "Video" button on my remote (which normally opens MC directly to Theater View), but instead of getting Theater View, I got the UAC prompt. The mouse was across the room, firstly, which was annoying. But then, once I approved it, I had to wait (and she had to wait) for the install process to finish before we could watch our show. I want to be able to do updates automatically on that machine, but there are some instances where it isn't appropriate and I just need to get going and use the application. Clicking "No" once is a heck of a lot faster than approving a UAC prompt, waiting for the MC installer to extract itself, and then saying "Cancel" (by then you might as well just do the install since the extract is basically as slow as the full install on my machines).
2. In the same instance, I could have said No to the UAC prompt, and then the install wouldn't have proceeded. However, I had no way to know at that moment that the UAC prompt was actually caused by the update. It could have just as easily been MC trying to register the JRTools.dll or fix FFDSHOW or install LAVFilter (I did get additional UAC prompts from the new build once it finished installing as well). So, I didn't know for sure why the UAC prompt was coming up, only that I was trying to launch MC (which I trust), so I said yes.
3. If I want to skip a particular build, or hold off for a while, there's no real way to tell what you're updating to from this process. I'm on the Beta team. Most of the time these builds are fine for direct production use, but occasionally (like with the recent Theater View changes), I need to do real work to get something fixed beforehand. Or perhaps, something known is broken in a beta build that I need, so I want to wait on it (at least on my HTPC). But, with the auto-update, there is a danger that someone else (my wife) will just blindly proceed through a pending install that I want to hold off on for some reason or another. Most of the time it is fine, but sometimes it isn't. So, if it asks before updating, there is an easy way to skip it quickly and initiate the update manually later when you are ready.