We are considering the pros and cons of switching from XHTML 1.0 Transitional to HTML5 for our website (for instance, to enhance our SERP positions by using microdata and new specific HTML5 tags for better indexing by search engine crawlers).
The current web pages are well-formed enough, so specifying
<!doctype html> and some "polishing" is the only thing we need to do.
However, as we can see from the stats for our website, many of our visitors are still using old versions of browsers like IE8 (7.3%) which may know nothing about HTML5.
The question is: can changing our website to HTML5 cause serious rendering and usability issues?