A good article on the topic can be found at Mike Taulty’s Blog post Silverlight *versus* HTML5? Really? He gives a short overview, before he goes into a more lengthy detailed discussion on how they complement each other. There are also a lot of comments.
When creating a new view the “Group by” function does not include “Content type” column. I’m sorry to say that this option will not be available in SP2010. (It is possible to do some work around with SPD, but they will disappear whenever the view is edited in SharePoint.