I use the FIR image replacement method in the Nav for www.message.uk.com I liked the fact that it gave me more control over how the nav displayed in standards complaint browsers, however in older browsers and user agents that don't support the advanced css, they just get a list of links. The only problem is that if people come to the site with images off, the nav is unusable. Not many people surf with images off but some do. Either because they are on crappy connections or because they have to pay for their bandwidth downloads. However it still is a problem. I wanted to use the FIR method on the blog I'm building (www.andybudd.com/blog/), however have decided to stick with images because of the above reasons. However it means that it'll be more complicated to do things like style switching if the images are embedded in the page rather than brought in externally in a style sheet. That's the real power of the FIR method and it's derivatives. It's not a question of why you would want to swap an image for text. It's about allowing you to swap images with other images in the CSS while still keeping the meaning and integrity of the original document.