Once notorious for its limitations, HTML5 is offering more than just cross-platform support. And it will only get better from here.
Web Open Font Format (WOFF) is gaining popularity, especially through Fonts.com, Typekit, and Google Web Font API. By using web fonts, devs and designers have more options with their text and therefore do not have to use images to get the look that they want.
And we all know that text is a HUGE part of apps and web sites. By having more freedom with something that is so indispensable, UI will in turn become more expressive, thus also benefiting users as well.
HTML5 Boilerplate first released in 2011 is being used for a growing number of websites, providing devs and designers with a great kick-start "template" they can use when implementing HTML5 into their projects. They can use as much or as little as needed from the template allowing for freedom, while providing devs with the basics, supporting lighttpd, Google App Engine, NodeJS, Apache, Nginx and IIS.
We can only expect that devs will be provided with even more frameworks and toolkits in the future (ehem, can we say, "DaVinci"? =P) adding to HTML5's new world of possibility.
Even nay-sayers will have to admit that HTML5 is on the rise, while Flash and third-party plug-ins are dying a slow and painful death.