As you know the web is a pretty dynamic place filled with plug ins such as Flash, Java and Silverlight but say good bye. Version 5 of HTML is being developed as you read and Google (the owner of YouTube) has launched their HTML5 beta program. This means that all the YouTube content is all shown in HTML5 instead of what is currently used which is Flash.
To enter this new beta program just head over to YouTube.com/HTML5 and click the join beta program and to leave just click the leave beta program
Flash is a long standing platform and is now at version 10 witch mens that it is all pretty smooth. But the only problem is that Flash is heavy and takes up allot of your computing power. This is why netbooks cant render flash properly. But again with HTML5 this problem will not exists and you will be able to render videos in HTML5 even on your iPhone, iPad or low power netbook.
You will need a HTML5 capable browser such as Safari, FireFox or my recommendation Google Chrome. And so thats HTML5