(non-expert here as well)
HTML5 offers 2 main advantages the way I see it:
- more "native" experience using animations and access to mobile features
- offline storage !!!
If you don't need it to look like a native iphone/android app, and don't need to store lots of data, then HTML5 is not that important.
However, if you want to create powerful "applications" for mobile devices in the future, then using HTML5 will probably be best (even Microsoft believes that HTML5 is the future, even over their own Silverlight).
If you want something "today", you should stick to current technologies. If you want something "tomorrow", then I would consider HTML5... but as ralph said, it isn't finished yet...