I'll piggyback on X's comments re: tables. Civi does render a lot of content as tabular data, which semantically justifies the use of tables. Where I think divs are most needed is the higher level page organization, which is properly a layout issue, not data.

The biggest issue I've run into when styling tpls with css is that there's currently a lot of inconsistency. Divs are used in some places, tables for field layout in some, dl/dt tags in other places, and descriptive tags (label) are not always applied consistently (e.g. the table class may be different so the cell tag is applied differently). In order to create a consistent layout, for even something as basic as an event registration page, you have to do a lot of work in the tpl and css just to bring the markup tags in line.