I've had one piece accepted by them, and several that I submitted for which I never received any news at all.
A friend had the same experience, and then quickly had 2 accepted almost simultaneously (for two different editions). We decided we think this is part of the trick: Avoid just submitting to the editions on the website that do not yet have a deadline posted. Submit, instead, to the books that have been given definite deadlines. You can be fairly certain those books are moving forward in the not-too-distant future. Both my friend's and my acceptances were for books that had a looming deadline.
Also Google the title of an upcoming Chicken Soup book with a deadline and see if an editor for that edition has a website up. They will sometimes list sample stories, chapter titles, and an email address where you can submit your story rather than just submitting it to the regular Chicken Soup website. That's how mine got in CS Shopper's Soul -- I didn't send it through the regular website.
My friend and I could be wrong about this, but that's the way it seems to us based on our experiences . . .