What are the usability, accessibility, screen-reader, or any other development, functionality, or cross browser issues with ?
Is there an
If you have a single Iframe, there would be little issue. However, multiple iframes compound the problem. A point of focus is not clearly available and the screen readers are not intelligent enough to find visual correlation (same reason why tables are bad for design). ARIA is an attempt being made to resolve some similar issues. YUI plugin link has more information.
However iframes do find their place in design. In one project I worked before, the page contained two iframes (one of them hidden) and the hidden frame was used to download an authentication applet. This doesn't add any accessibility woes as the point of attention is limited to a single iframe which seemlessly merges with the page