Firefox >= 3.5 lets you use SVG filters (and masks) on HTML content, per this article. It doesn't work on other browsers (at least not yet). With the Filters menu in Inkscape 0.47 it becomes even easier to do, as described in my tutorial:

http://www.peppertop.com/blog/?p=824

For an example of what I'm referring to, the image below is just HTML text with Inkscape-derived filters applied. The text is still selectable, indexable and available to screen readers - it's just plain-old HTML.