Web 2.0 - What is it really?

After reading a number of articles on Web 2.0 I've come to the conclusion that Web 2.0 is whatever YOU decide it is. One article described Web 2.0 as a "meme" (http://en.wikipedia.org/wiki/Meme), basically and idea or concept that spreads from person to person and evolves over time. Some parts will expand and grow, others will wither and die, depending on the end users, much like evolution in the "real" world. One aspect of Web 2.0 that I particularly like is the concept of sharing. I have long been a fan of the Open Source movement and this seems like a major development. Now, instead of downloading a free program, with the inherent risk that it will mess up your computer, you will be able to try things online, in real time, without having to take the risk of harming your computer. I can also see this as a real boost for operating systems such as Linux. Although Linux now comes in many flavours, many people (myself included) won't take that leap. With so much being available online, there is much less incentive to purchase software.