The fact that most Mac users don't use many apps on their laptop, beyond what's built in, and what they do use is probably free is the one thing that makes me think the app store bubble will blow over.
That doesn't seem to be the story on the iPhone OS devices, though. Everybody I've ever seen with one, regardless of tech savvy, has it loaded down with apps and is excited to show off their favorites.
Mobile apps tend to be "bite size" (approachable), centrally discoverable through the App Store, very low cost, be built around rich media, and the user feels a control over their management that makes the experience more like the "lightness" of visiting a web page than the "heaviness" of traditional desktop app management which is marred by unpredictability, multistep install processes, reboots, conflicts, and a general feeling of lack of control. I think users really like software... they just hate all the bullshit overhead that has usually gone with it.
