web 2.0 has been a loose term tossed around for the past few years really... came in on the tails of the major browsers fully supporting cascading style sheets and agreeing to follow web standards as put together by the ( World Wide Web Consortium (wc3) )... what was html is now usually css... was was perl or javascript is now ajax (which is basically super javascript)... thus 2.0... also relates to large strides taken regarding the DOM, xhtml, xml, etc (that last one there doesn't involve any scripting ;-)
I used to stay in a lot
there's also a "look" to whats termed web 2.0... and people like to make fun of it =)
really the same old, nothing ground-breaking anyways as it all happened so gradually... likely sounds good when you're pitching a client or trying to pick up chicks