As well as helping screen readers, using CSS means alternative devices like mobile phones and PDAs can show your content effectively and easily. Although the current market in the West for browsing the Web through mobiles is small, it is growing and by using CSS you can create a Web site which is easily viewable on these devices with little extra effort,. So as more people use them it will be simple to convert your site to work with current or future devices..

Downsides

Currently, Web browsers treat CSS slightly differently, so when your Web site is created you may need slightly more cross-browser testing, and you will need to find a Web designer who understands how to build a site in CSS correctly. Most professional designers and developers are now seeing the benefits of creating standards based CSS sites, but it is worth ensuring that anyone you hire to make your Web site does know CSS before starting a project.

But the downsides are small when compared to the immediate and ongoing benefits of a CSS-based Web site.