Of course we are talking in general terms so get on facebook etc are not great answers. Is there anything you do on the internet now that was impossible 10 years ago?
Now vs. 2003? I'd probably have to say that you can make all your purchases online now. Sure, you could make clothing purchases in the past, books and whatnot, but you'd never seriously consider stuff like your grocery shopping.
I can buy a snow blower online and have it show up a day or two later assembled and with gas in it ready to go.
I do a lot of web programming, so I get to use Web Sockets, Web Workers, WebGL (although I don't really know much about WebGL, it's there if I want to use it), and Node.js. I'm pretty excited about WebRTC, especially the pure data channels, but that's not entirely standardized yet, so it doesn't exactly apply to the question. In the actual ways I use the Internet, I agree with minimum_wage, nothing's really changed. Then again, Ajax/Comet is more widespread of a technique. Oh, and gmail.com went live in 2004, so that counts for something.
Definitely live steaming. The ability to watch, for instance, a robotics competition that wouldn't have made it to TV is really incredible. It allows people to watch things live that would otherwise not have made it to a mainstream form of media. Youtube has had a similar effect, only with pre-recorded videos.
Regularly talk to people I know who are from the other side of the world
Yeah, IE6 was pretty innovative...so it's pretty easy to conclude that...long live IE6! http://www.saveie6.com (IE6 was the first browser with Ajax, right?)
I cut the cord to cable/dish a few years ago because it was too expensive for content I didn't watch. Last year the local telco offered a fiber connection and a great introductory offer to their TV service. We did it for the 2 weeks of the Olympics, but found most of it was available streaming on the web. Between the Redbox and online streaming services (Netflix, Hulu, etc) we found we didn't watch live TV. Watching YouTube 10 years ago was painful on my dial-up connection. Today between 3 iOS devices, Wii and the XBox 360, we are all streaming video and no one on a traditional computer.
Upload weeks worth of music and stream it at 320kbps without incurring massive fees.
Use Photosynth to automatically stich my photos together into a muliti-level 3-D collage and, separately, a point-cloud model of the environment. Sadly, the site hasn't been updated in years. Still one of the most impressive things I've seen on the web. 20 gigs free storage, simple to use, amazing results. I don't work for them, just a fan. Check out this guy's perception of German architecture: http://photosynth.net/view.aspx?cid=e4ffb607-d80a-48f2-a523-...
Most of what I do on the internet has not fundamentally changed in the last ten years. There are small variations with the websites or software that I use, but general themes of communication, information, file sharing, shopping and gaming are still my principal online activities. How I do those things has changed significantly with the development of stand alone apps and smartphones.
Think this is the answer most of the examples seem to be quantitative not category differences .