One of the topics that comes up regularly in the context of Web 2.0 is the idea that social software gets better the more people use it. Tim O’Reilly wrote about it when describing Web 2.0 and brought it up when he was on stage with Bill Gates at MIX06.
Tim called it a principle of Web 2.0. But I don’t think getting better with use is exclusive to social software. Alan Cooper wrote about building software that learns how the user works and optimizes itself for that usage pattern. For example, Windows Vista has a new feature called SuperFetch that “understands which applications you use most, and preloads these applications into memory, so your system is more responsive when you first boot or when you switch to a different user profile.”
The big difference that I see is that personal software has to be designed to learn where social software automatically improves with use.