I've been toying with the idea of reworking my website, not because I use it particularly often, but because I wanted to have a not too complicated programming project and look at some of the technologies that I've not had any time to keep up with in the past few years.
When I originally designed my site, IE6 support was still a real consideration. Which meant no transparent PNGs and no CSS niceties like max-width. While AJAX existed, the built-in support in ASP.NET was quite bad (if you recall, it was centered around sending full HTML components). JSON was not in common use yet, so I ended up writing my own custom AJAX library built around .asmx services and client-side XML parsing (which was lots of fun considering IE is the only browser that reliably implements XPath so I couldn't use that). JQuery was still years away.
Now though, I'm using ASP.NET MVC 4, EF5, HTML5, CSS3, jQuery, Modernizr, knockout.js, and Zurb Foundation. And I can't believe how much this has evolved. Now, if you've got a requirement for the site to look and feel the same on older browsers (particularly anything before IE9), I think you're going to be in a world of hurt. But if you have the luxury of being able to target the modern stuff, it's really amazing how much better things are now.
It's also very helpful that for nearly everything I've needed so far, I could just easily find it with NuGet and drop it into the project with minimal effort. It makes it much more painless to use all the different libraries.