I think I may have submitted some stuff to them when I was in college to no avail or response. BUT, they publish worlds of great stuff. My favorite full series...Dragonlance used to be TSR till Wizards of the Coast bought them. Plus, they do Magic the Gathering which I adore.
It would be fun if one day they picked up one of my books. I know typically they are big-series based, but that's about the extent of my current knowledge.
If you check their pages I'm pretty certain they only do stuff to support their product lines. Mirrorstone is their YA and other stuff imprint but I haven't check them in awhile. I haven't heard anything bad about them which is usually a good sign and Paul S Kemp (Ervis Cale Trilogy) has great things to say about them.
I have considered sending a sample off to WotC for years, but never plucked up the courage. I am just not really sure what they want with a 10,000 word writing sample: at first, I thought about sending them a snippet of one of my fanfics, but then thought 'no - they might not like me messing with established stuff'. Then I thought about writing a D&D based short story... but again, ditto the first worry. So I thought about sending them a bit of my current novel... but then I worried that I would need to show then that I understood how their worlds worked. So in the end, I tied myself up in knots with stupid worries and concerns and never got around to just, you know, shutting up and getting on with it.
I might try again, though - I think I might dig out the 10,000 word sample I wrote ages ago, give it a damn good editing (it will need it!!) and send it off. If I may, might I post it on this forum when it is ready, good sir?