We use them all the time in our program(s).
They work well for us, anyway. You can read more on my blog or get my free ebook in my signature here. It’s a pretty broad topic. Here are some other resources worth checking out:
NPA Velocity Plus Program - I think this is the canonical source for this program despite the fact I’ve seen it linked/written about/available for purchase in a bunch of spots (http://nationalpitching.com/products.html). Anyway, it uses “holds” and “throws” of weighted balls up to 2 lbs and as light as 2 oz.
SETPRO’s BWBK - I don’t think you can buy this anymore from Paul, but here’s some info (http://setpro.com/forums/showthread.php?t=2480) that I was able to find.
The Athletic Pitcher - Ron Wolforth’s program which uses TAP weighted balls. It’s a lot more than that, of course. http://www.theathleticpitcher.com/
I have a free eBook in my signature as I stated before as well as my own brand of weighted balls for sale. I have a book that uses weighted balls but it is meant for youth pitchers, so it’s not useful for you.
Anyway, that’s just a few things I found. Good luck with your search!