HTML5 and CSS3 has been exaggerated and even abused for marketing purposes. It's certainly true that HTML5 is evolutionary rather than revolutionary but it addresses so many obstacles for web development that i believe the impact will warrant the hype. There are some major technological advances such as HTML5 WebSockets and the popular video and canvas elements but i think the real advantages will come from CSS3 (the style sheet mark-up language that accompanies HTML5). CSS3 will allow designers to make very rich interfaces with relatively little effort and without the need for any third party plugins like Flash.
With these two standards specifications in place, web applications rather than legacy PC applications (as Google calls them) should become a very viable option. There was another bottle neck for web apps however and that was the inability of web browser's of the time to render rich content, quickly. Web browsers were never meant to run such rich, interactive applications but Google quickly addressed this by creating Google Chrome which was primarily designed for speed. Chrome is a major achiever in all other aspects as well, such as security, stability, etc. but it was never intended to steal market share, it merely had to be competitive enough to force the other browser makers to follow suit, and they have. All major browsers such as Firefox, Opera and Safari have caught up and are matching and even overtaking Chrome in speed, security, technology, et al. all except one browser; Internet Explorer.
With the issues of functionality and speed addressed there exists one last obstacle to web app development; one needs to consider how big the potential market is and Microsoft Internet Explorer still holds around 60% of the browser market. That means we can't build nice rich web application unless we are willing to exclude 60% of the online population which would be about one billion people. So why is Internet Explorer so far behind? Is it because Microsoft have lost the plot and don't know what to spend their mountains of money on? I think the likely explanation is that Microsoft is aware of the degree of control they still have here and are using it to prevent people from moving on to the web and away from Windows dependence. This is a decisive battle between Google and Microsoft, i find it amusing how Apple is biting at their heels trying to impose their presence in this situation. Apple has backed HTML5 which is peculiar since they (as with Microsoft) also stand to lose market share in a platform independent world.
Here are some reasons to stop using Internet Explorer:
CSS3 Fail Whale - Works in every browser except IE
Video and Canvas - Won't work in IE
Google Gravity - Some browser physics
Select a new browser:
Google's browser selection page
Microsoft's browser selection page
Compare HTML5/CSS3 browser support