There are cross browser compatibility problems with both tables and div layouts.
I have used both, and in a lot of cases the div works better than tables for a lot of things and it is worth learning, along with all the other CSS techniques. However, using tables for what tables are meant for (that is... tabular data) is generally a good thing.
However, I came up through the days when the table was about the only way complex pages could be put together, and I have a great deal of XSL I've put together over time for generating HTML tables so I still often use that.
I consulted on a project where it was mandated that tables would not be used, and where there were a number of browsers that were required for compatibility - and we ended up using just about every hack we could find (from sources such as the CSS Hacks and Filters book by Joseph W. Lowery as well as dozens of other books and web sites). They spent a lot of money forcing the CSS Div mandate over using tables where appropriate.
Woody Z http://www.learntoprogramnow.com