Much like CSS3, widespread adoption for the next-gen web languages is a distant mirage. Still, it is important to stay educated on these things and even participate in these early stages while things are still malleable. Rather than re-hash everything here, here is a roundup of articles talking about the two major new "competing" formats.
There is also a new poll in the sidebar where you can cast your vote as to which one you prefer at this point, or if you just don't care.
What everyone wants to avoid is another standards war. Fortunately, since both languages support XML namespaces (or, in the case of the HTML serialization of HTML 5, DOCTYPE switching) it's unlikely that we'll see the sort of browser dependent behavior we did in the 1990s. Standards wars aside, the future looks bright for web development. These new markup features and APIs will provide a rich environment for web development that should narrow the gap between Web and Desktop applications.
Both X/HTML 5 and XHTML 2 are competing to replace HTML 4 and XHTML 1. Even at this early stage of development, some browser vendors have already stated their preference for one spec over the other. As a result of the haste and closed nature of deliberations, this issue is starting to polarize the Web standards community. As the two specs progress, more development and marketing dollars will be invested into one spec than the other, and all the ingredients are in place for a standards war.
The only thing that is certain about the 5 August 2002 working draft of XHTML 2.0 is that nothing about it is certain. It will almost definitely change in some way between now and adoption as a recommendation, but the goal of emphasizing structure and semantics isn't likely to change. For this reason, it's a good idea to take a look at the pages you build now, and start getting into the habit of using structure and styles appropriately. Use markup to designate what something is, not what it should look like, and use CSS to do the rest. Overall, think more about the structure of your documents and what you want them to do, and not necessarily so much about what they should look like.
Work on HTML 5 is rapidly progressing, yet it is still expected to continue for several years. Due to the requirement to produce test cases and achieve interoperable implementations, current estimates have work finishing in around ten to fifteen years. During this process, feedback from a wide range of people including, among others, web designers and developers, CMS and authoring tool vendors, and browser vendors is vital to ensure its success. Everyone is not only welcome, but actively encouraged to contribute feedback on HTML 5.
While XHTML2 is a semantic improvement over XHTML 1.0, it does not seem likely that it will matter for web developers for a long time, especially when one considers that Internet Explorer still doesn't offer XHTML 1.0 support. It will take many years for a new version that might support XHTML2 and we have been given no indication that the next one will. On the other hand, many parts of HTML5 are already creeping into browsers, and, if Microsoft takes an active part in the development of HTML5 in the future, it looks likely that many features that are already very polished will be supported cross-browser in a much shorter timeframe. The fact that HTML5 contains several areas that are already ready for implementation while still being developed in other areas makes it a technology that is easy to partially adapt until browser support is fully evolved for the features you wish to use. HTML5 will be the future of the web, so my advice would be to pay close attention to it.
Check all of the CSS-Tricks polls and results over on the Polls page.