Actually, regardless of what some claim, tables still have a solid place in some layouts, which are quite simply impractical to work with being fully CSS based. Hacks are not always accepted in practice, and they should not be taken for granted, using them is a unique skill on its own, as they ain't always obvious.
Equal-height column layouts with a header as well as a footer would be another example, and this is where i would say that it would be fine to use tables, as the known CSS methods are quite complex.
But other then that, there really isn't a good reason to stick with tables for layout. It would be far better to avoid the cases where we would need to resort to tables.
The place where it becomes problematic, is where we have rich containers with borders, that must be scratchable at the same time. There is a position based technique to do this, but tables would still be better when having older browsers in mind.
The separation of content from style is not entirely possible yet, some layouts would still require extra markup, this would usually be in forms of division elements, like in the above technique. And again this is where we have a few arrogant web designers, wo criticize the use of "divitis", both the alternative is however worse, and note that screen readers as well as SEs simply ignore these additional divs, it dose however add a few bytes to the file-size.
While there are some coding specific changes you can apply for better ranking, those are mainly focused on headings, emphasized text, internal links, as well as outgoing links. You should be using headings in the correct order,
h1 for the main heading,
h2 for subheading of
h1,
h3 for subheading of
h2, Etc.
There is no
SEO releted benefit from using XHTML instead of HTML, or having a fully CSS based site instead of table based. Those are likely to be rumors started among novice designers.