There's one piece of advice SEO mavens always give out that always sets my hair on fire. It's this: "Always design your web pages with CSS. No Tables!"
This advice is pure, unmitigated bullshit.
I just designed a website for a client. I used CSS for a lot of things. Surprisingly enough, I used tables for-- gasp-- tabular data. A table of classroom assignments. A table of type/key/value tuples for features of the software the students are writing for each assignment. Tabular data. That's what tables are for.
SEO experts who terrify newcomers into thinking they're doing something wrong when they use a table-- a perfectly useful tool intended for the liquid display of tabular information, the outer perimeter of which can be affixed to whatever grid makes you happy-- do nobody any favors. Be specific. Say "Don't use tables for layout. Learn about semantic design. Use tables for what they're good for."