thanks very much for your quick answer.
i'll keep an eye out for the next version of the premium plugin, that functionality is exactly what i need.
for the second, here's an explanation: the site will contain 1000s of book reviews, where
post_title is the name of the book and
post_content is the review. there is a taxonnomy called
by where the term is the author's name (the author of the book, not the wordpress post author). the author's name will not appear in the post_title and most likely not in the post_content. so we'd love to have a "search by author" option which only searches the author taxonomy terms, but from what you say it doesn't seem possible.
so i think i have a solution: i will hook into
save_post and add a custom field containing exactly the same data as the taxonomy term, so i can then do a custom field search, e.g.
if i'm missing a better or more obvious solution do let me know!