- Web 2.0/AJAX is nothing new, but there are more and more companies or web developers putting these buzzwords on their web site without any knowledge of these techniques.
- The wrong use of Web 2.0/AJAX will prevent some users to visit your web application. If you want to make all of your visitors happy you have to build two versions of your web application (i.e. if JavaScript is disabled). This we had to do in the past, too! Do you remember? If you are using controls or frameworks that will do this for you automatically and the correct way you are fine, I didn't find any.
- Using frameworks for AJAX is a great thing, because you don't have to look for all the details and problems. I found some web pages using frameworks that bloated the traffic to save some bytes when invoking AJAX methods. Use Fiddler to calculate the complete traffic your web application is using and how much you will save if you are using AJAX. The same is true for Web 2.0 frameworks. Sometimes it is easier to use your own JavaScript instead of big JavaScript files (where you only need about 1%).
- You should watch out for updates of your web application. If you are using AJAX there may be requests during your update that may fail. Use error handling where you can. Have a deep look inside your code (and the source code of your used frameworks) if interfaces will change. A new version can stop old opened web pages running.
- More and more web sites using AJAX to completly update the page without a postback. If you press F5 (reload) you will be on a different page. Yes, I know there are some frameworks/libraries that are working correct. If I want to open the "Contact Us" link in a new window (Shift + Click) it will fail, too. Have a deep look on your log files and track visitor ways.