Microsoft's World Wide Telescope is an amazing piece of software. I installed it on my 8-year-old son's computer yesterday, and he spent a long time exploring the universe with it (and he said he can't wait to use it again).
What's also amazing is the explanation of how to download and install WWT:
This strikes me as an excellent example of why desktop software is paralyzed by fear. Unless you're a power user, your reaction to this will be, "holy crap, I have no idea how to do all that!" And then you'll search Google for a web site that does what you need without requiring so much work.
Those of us who believe that desktop software is still relevant in a browser-based world should be up in arms about how hard it is to install software (on Windows, at least - it's easier on the Mac). Multiple security warnings, required OS updates, and tech-heavy language make downloading and installing software too scary a prospect for non-technical users.