[pault]

Aside from the semantic HTML movement, they're clunky and verbose, more difficult to break up into reusable components, and table rendering is more expensive than the equivalent layouts with non-table elements and CSS (at least that was my experience last time I tried profiling a table with hundreds of rows).

Edit: they also have a lot of intrinsic layout behavior that can be difficult to predict once you start getting into more complex layouts than header, sidebar, and footer.