A few years ago, I read a bunch of those "advice for authors" books. They all agreed that in a good query letter one MUST mention a few books from the publisher's backlist and a GREAT query letter also mentions why those particular books are wonderful.
So fast forward to today - I've actually got writing credits now and I like to keep my query letters short. Is it all right to assume that editors KNOW what's on their backlist and KNOW they're good books? It's not like they'd publish junk!
I always CHECK the backlist to make sure my book is a good fit, but I'd really rather spend the query talking about MY book... not what they've already published.... somehow it doesn't seem like a good use of anyone's time to include a paragraph like:
Your firm has a history of publishing fabulous picture books involving meter and rhyme. I especially liked Peach at the Beach, Carrot in a Garret and Babbage the Cabbage. I think my book, Celery in Hell-ery would be an excellent addition to your luminous list!
So, what says an actual editor who has to read millions of these things?
Your pub credits are much more interesting than praise for our list (assuming they're credits at houses I'll recognize).
But for those of you reading the blog who haven't got any pub credits, don't bother including a paragraph like the one above. If you're going to show that you know what the publisher publishes, it involves more than mixing some titles with some positive adjectives. Say why the books you mention are good, or talk about something else.