Personally, I do not have a problem with the term "web two point oh", except when people don't know why they're using it, or what the term itself means. Many people argue, however, that "Web2.0" doesn't actually mean anything and is simply a marketing term: fine, you win, it is. But what I say is, Why are marketing terms bad? First of all let me say what I think Web2.0 is.
Web2.0 is not a technology, neither is it a collection of technologies (strictly speaking). I believe it is simply a set of "best-practices" and "design conventions" which help every end user and provide a rich resource of information in a usable, interactive and fun environment.
Best practices refers to valid, semantic HTML and design driven by CSS. It also includes having input and device agnostic behaviour, such as an obvious tab-order and skiplinks. Design conventions means following the pack. Scope out at least 10 websites, and see what the majority are doing, then copy it. This includes fundamentals such as "logo links back to the homepage" and the logo position is "top left" in the design (for Western-aimed websites). In the first few seconds every user should be familiar with the navigation and have a fail-safe escape of getting back to the homepage - these conventions make this possible. Following these rules you make your website both accessible and usable to the end user. Whether this means Joe Average or someone using an obscure assistive technology you've never heard of, conventions help everyone.
Making the information available is also a fundamental of the "Web2.0" 'ethos'. The first stepping-stone in making the information available is making it accessible. Hopefully this has already been tackled with the semantic conventions discussed above. A second, but still fundamental way of making information available is through APIs. Many sites are using some kind of API already, whether this be just read-only in the form of RSS/Atom feeds.
'RSS' feeds (I'm not leaving the Atom group out here, but RDF Site Summary sums up the technology, so I continue to use that abbreviation to denote 'web-feeds') are a great tool for making information a valuable resource. Having RSS, a 'read-only API', allows users to take that information and have it presented however they see fit. Whether it be on their own website (some copyright issues here), on a "personalised homepage" like Netvibes, Microsoft Start or Google 'IG' or even on a "mashup" website (which uses feeds from numerous sources to provide new ways of grouping/sorting/reading the information). This means the information can be presented in an interactive manner, especially when combined with other data, to provide a fun experience for the user.
Tom Coates showed some funny slides of "Web2.0" websites at the Carson Summit about the Future of Web Apps, depicting "Web2.0" as 'gradients, rounded corners and large fonts'. Although, this is a funny statement, there is some truth in it, especially if you look at a few "design conventions" (see above). And maybe this is where these trends have come from. But, rounded corners and gradients make sites look friendly and invites users to interact and large fonts make the site easy to read, and therefore the information appears more accessible.
Two other speaksers from the conference, Joshua Schachter creator of Delicious and Cal Henderson (Flickr), are both involved in so-called "Web2.0" applications which make use of 'tagging' as a form of grouping and sorting information. This is another outsiders association with "Web2.0" sites, and definitely has some weight. Tagging is a convention because it is simplistic, fairly easy to understand and encourages user involvement. It's the most basic way of grouping and describing 'things' ('red balloon sky' for example) and finally, it allows good aggregation from differing data sources.
Finally, "Web2.0" sites mostly try and behave more like conventional desktop applications. With a less stop-start post/refresh behaviour and a more fluid interaction. Most "Web2.0" sites/applications provide social services, such as sharing photos or bookmarks, but these sites don't restrict themselves to the confinds of their website, or even the restrictive nature of (conventional) web browsers. Websites such as Flickr have desktop applications to help the user contribute to the website without using their web browser. They also give the ability to upload photos from mobile phones. Both of these technologies help the website solidify it's perceived purpose, as an application.
In summary "Web2.0" is simply best conventions (both markup & design) which allow users to easily find, organise & combine data in an familiar, accessible yet beautiful environment.
OK, so I've waffled on about what I think "Web2.0" is, now let me say why I think it's good for me, and the web.
All of the ideas already discussed and conventions coupled with the forward thinking nature of the people developing and innovating in the "Web2.0" scene are going to push the technologies for web of the future.
...there have been two kinds of people in the world - people who think of the web as a browsable information resource and those that have tended to view the web as analogous to a desktop application. Jesse (James Garrett) made a point ... that the web is being framed in terms of things that people have known before and that we're still determining what the web actually is. And what it's gradually revealing itself to be is neither (information resource / application) and yet both. It's something new which we have to craft for in a new way. Very much liking that - it's like the distinction between document and application has collapsed and is now being rebuilt and reconfigured from the ground up.
I think being in and around the web scene now is a very exciting time. There are hundreds of ideas being thrown around, thrown out and thrown together. The reason I think "Web2.0" is beneficial to the web as a whole is; firstly, there is capital being injected to help people innovate and secondly, those innovations are being widely spread to corners of the web (through mindless marketing with terms such as "Web2.0") which are usually reserved for us geeks. The second point helps the growth of the web, and also feeds point number one. Hopefully this can start a snowball effect and help the growth and future of the web for everyone involved. It's an exciting time and I'm lucky to be part of it.