...can you use them with a plastic drop in bobbin?
All of the tutorials I've seen have been on the older style metal bobbins with the type of bobbin case that you put in and out every time you change the bobbin...

According to this FAQ, yes:
http://www.daystyledesigns.com/magicgeniewashers.htm

I use them with my janome plastic drop in bobbin. I think they may be helping my stitches when fmq. I just leave it in all the time.

Where can you buy them? I tried JoAnn and nobody had ever heard of them. I asked for them by the correct name, too. The person I asked said she hadn't heard of them and called someone else on her phone and asked and again, no. It really got funny after that because the ladies started calling out to each other from one end of the store to the other -without phones- and then back to me to see if I was sure I had the right name and it went on and on for a few minutes. At the end of it all, no Bobbin Genies. :(

I use them with my Viking drop in plastic bobbins.

I use them with my Janome plastic drop in bobbins. It has helped with my regular sewing stitches.
I leave one in all the time.

I purchased mine from Nancy Notions

GREAT question - I've wondered this many times myself. Thanks for asking and thanks to all who replied for all the helpful responses! :-D :-D

ok...then i guess i'll take the plunge and try them! thanks to all who answered! Donna

Tropical, Clotilde's has them:
http://www.clotilde.com/list.html?criteria=bobbin+genie
and so does Amazon:
http://www.amazon.com/Little-Genie-M...dp/B004KZ27QG/