Why tables for layout is stupid:

Tables existed in HTML for one reason: To display tabular data. But then border="0" made it possible for designers to have a grid upon which to lay out images and text. Still the most dominant means of designing visually rich Web sites, the use of tables is now actually interfering with building a better, more accessible, flexible, and functional Web. Find out where the problems stem from, and learn solutions to create transitional or completely table-less layout.

The problem with using tables:

• mixes presentational data in with your content.
  
  • This makes the file sizes of your pages unnecessarily large, as users must download this presentational data for each page they visit.
  • Bandwidth ain't free.
• This makes redesigns of existing sites and content extremely labor intensive (and expensive).
• It also makes it extremely hard (and expensive) to maintain visual consistency throughout a site.
• Table-based pages are also much less accessible to users with disabilities and viewers using cell phones and PDAs to access the Web.

Modern browsers are much better at rendering Web standards and we don't need to use these archaic methods any more.

Instead of nesting tables within tables and filling empty cells with spacer GIFs, we can use much simpler markup and CSS to lay out beautiful sites that are faster to load, easier to redesign, and more accessible to everyone.

By using structural markup in our HTML documents and Cascading Style Sheets to lay out our pages, we can keep the actual content of our pages separated from the way they are presented.

This has several advantages over using tables....

Redesigns are easier and less expensive

By removing presentational markup from your pages, redesigns of existing sites and content is much less labor intensive (and much less expensive). To change the layout of the site, all you need to do is change the style sheets; you do not need to edit the pages themselves at all.

Using Web standards reduces the file sizes of your pages, as users no longer need to download presentational data with each page they visit. The Style sheets that control layout are cached by viewers' browsers.

Reduced file size means faster loads and lower hosting costs.

Using Web standards also makes it extremely easy to maintain visual consistency throughout a site. Since pages use the same CSS document for their layout, they are all formatted the same.

This strengthens your brand and makes your site more usable.

Using Web standards makes our pages much more accessible to users with disabilities and to viewers using mobile phones and PDAs to access the Web.

Visitors using screen readers (as well as those with slow connections) do not have to wade through countless table cells and spacers to get at the actual content of our pages.

In other words, separating content from the way it is presented makes your content device-independent.

Speaking of accessiblity, minimizing your markup and using header tags properly will also help improve your search engine ranking.

Reducing the ratio of code to content, using keywords in your header tags, and replacing header GIFs with actual text will all help your sites get better search engine results.