I've just had an experience I'd never dreamed would happen.
I knit a doily on size 000000 needles (yes, that's six 0s) using size 100 cotton. Looks like any other doily, no? Well, it's not. Click on the picture to see the stitches up close. Still not convinced? Try this one:
As you can see, that's a penny in the middle. Need more?
It's a little hard to see the white on white but if you click it, you'll see the little guy is the same pattern as the middle of the big guy. Big guy was done using regular bedspread weight crochet cotton, the stuff you see in all the stores.
I have to be honest and admit that I picked the absolute worst pattern to go micro with. Here it is:
Knit 2 rounds plain.
Knit 1, make 3 stitches in the next stitch.
Are you blinking kidding me?!?!?!?!
Yeah, make 3 stitches in 1. Repeats through the whole pattern. I had trouble doing that with the larger thread and larger needles. Ooops, forgot about that. Plus it's not lacy so you know I've got to try it at least once more with a lacier pattern.
Oddly enough the cast on wasn't the hardest part (I leave you to guess the hardest part). The needles are so small and so light, they just don't fall through the stitches like the larger needles can.