Woo Hoo Rosebush ! I harvested seeds last year and as a newbie who is WS Hosta, I'm thrilled to read you had success.

Fantastic! Isn't it amazing how hardy they are? I have only started them inside in the past but this year I'm winter sowing them.

Nanmol, You're way ahead of me - even though I have some large hostas, I wouldn't know how to harvest seed from them. :)The ones I sowed were received in a trade by a very generous GW-er.
Patrushka, Yes, I'm amazed that something so small could survive the weather we've had lately. And I'm thrilled because I have SO much shade! These little plants will have lots of room to grow once they're planted out.

rosebush - They are easy to harvest seeds from! You have to leave the scape (the tall stem that the flower blooms on) on the plant. If you watch it, you'll see seed pods forming once it finishes up blooming. They will be green for a long time before changing over to brown (and then the pod will start to crack open). Wait until they brown before you pick them. They get really large, I want to say off the top of my head, about an inch or two long. You can't miss them. Not all hosta produce seed and the only way I can figure out which ones do and which ones don't is to wait and see. I have a yard full of the common green/white plants that don't! I love hosta plants, they are so easy and so forgiving as you just found out!