Okay so I don't know a whole lot but I was first introduced to them when Ember (and Susannah) posted about making stamped/beaded pens Pennywise Arts ~ Online PWA Class Archives ~ Stamped and Beaded Pens
You can buy them at Michaels in the beading section but if you do want to purchase some they are much cheaper at Pennywise Arts
I already know some of you ladies are thinking "oooh micro bead swap"
I got a 5 oz bag of clear ones and some sheets of o'so sticky tape (which is awesome super tacky double sided adhesive) I made about 10 beaded pens and I've used some in shaker cards (yes alicia that's what I used in my shaker cards in the swap) and I still have a ton left!
Check out the website they show alot of cool projects!