Look at the charts for IE noted by http://www.findmebyip.com/litmus/
It's really pathetic if you check it out. You either write forget HTLM5 and CSS or plow ahead thinking the future is really mobile devices and pads with Chrome or better browsers.
-> Know your market.
A while ago I was introduced to Media Queries and Responsive Web Design. My immediate reaction was "Wow - this will future proof any new site I manage and ensure it looks great too".
I tried pitching this to my head of IT and he's thrown up some objections. I'd be interested to get some thoughts on these.
The main objection seems to be that Media Queries rely on CSS3, which is only available in IE9 onwards therefore as the majority of users are on older browsers, it makes the technology redundant.