I can't find it right now, but somewhere in the webmaster guidelines, Google has pages explaining such things as how to name your images and how to write good links. They do recommend using relevant keywords to anchor the links. If you think about it, this is also what helps visitors. Imagine you're writing "Gray skirts are fashionable right now." If you want to link to a site that talks about what's "fashionable right now", you'd put the link on that text. If OTOH you're linking to a site that talks about (or sells) gray skirts, you'd put the link on "gray skirts." That way, visitors get what they expect after clicking the link.