pageoneresults - 12:27 pm on May 27, 2010 (gmt 0)
1) Will older browser display it OK (assuming I won't use any new tags, which I wont)?
2) Will browsers in Mobile Devices display it OK?
Google use an HTML5 DOCTYPE, it is meant to be backwards compatible.
You can use the new elements and do just fine, I've already got a handful of HTML5 sites out there and they are performing as expected. I use the new elements but I've wrapped their content in <div>s for now until support is fully implemented. I can still segment my documents semantically using HTML5 elements, the basics, and cover all my bases e.g.
There are some CSS rules to use so that the new elements are treated properly. There are a few articles out there explaining the use of those rules.
All of our new sites being launched use HTML5 templates. It's a tough call for us as we have many XHTML based applications. But, for static brochureware and/or promotional sites, HTML5 is just fine, go for it!