I would say the most popular deprecated tags are <u> and <font>. This is the web not a word document and underlines can make people think that the word(s) are links. As far as font a basefont size and color should be set in a stylesheet.

Dreamweaver 8 allows a user to add those tags into a webpage. That’s no good, shame on you Dreamweaver. If people are allowed to add <u> or <font> tags in their documents, then what happens when browsers no longer support those tags?

People should use CSS to seperate content from presentation, but people are going to take short cuts. I place the bulk of the blame on the editors. The people are always going to try to take short cuts so eliminate the short cuts and guide users to do the right thing.