I just answered this question. IE is the only browser that does not support HTML5 except with javascript help.
Very much depends on who will be viewing the site for me. If I was to create a site targeted towards those in the web design industry then I don't mind using some of the latest technologies but in general, nobody in the web development business will be relying on HTML5 or CSS3 until there are far less people using browsers that don't support them. As far as opinion of HTML5 goes without bearing in mind who can make use of it and who can't, I think its fantastic.
IE is to hard to work with. Stop supporting crap browsers and people will stop using it. Educate everyone you know that they are using the worst option out there. Otherwise the dead weight will slow us all down.