There’s a couple of things you have to bear in mind before adventuring on the new markup boat. HTML5 is not for everyone. Therefore, you must be wise and select how and where to use it. Think of all the markup flavours you’ve got available as tools: use the right one for the right job. Therefore, if your website is coded in standards compliant XHTML strict there’s no real need to change to HTML5.
There’s also the fact that by using HTML5 code right now your website gets stuck in some kind of “limbo” since even though your browser will render HTML5, it does not understand it as of yet. This may also apply to other software such as screenreaders and search engines.
Lastly you must consider that HTML5 is still under heavy development, and it’s probably the “most open” project the W3C has ever done. With the immense amount of feedback and all the hype around it, the current draft is bound to change and it’s impossible to predict how much.
So if you’re ready to do the switch, are not afraid of using technology that in the near future will be way more meaningful and can easily change whatever piece of code that might get broken, then keep reading.