I agree with Walter wholeheartedly. Here in New England, we were always told that RMJ and Ponderosa Pine didn't last long due to our high humidity and rain levels. Working with both these species for over 10 years now, I have found that they thrive here. Nick is right that the foliage is different on the RMJ (but certainly desirable).
Regarding Ponderosa Pines, I know of no one who has had luck with needle reduction though (has anyone?). Walter speaks of cutting needles - this is common with Ponderosa. Right now I am working with 3 collected shohin sized Ponderosa Pines (a crazy proposition, I know!). One of them does have a much shorter needle but i believe it is due to the stress it experienced while growing - as it gets healthier, I expect them to get longer.
Now with California Juniper, I have seen mixed results. There are a few at New England Bonsai Gardens that have been thriving for almost 10 years now so it can be done. I have just not personally tried them here yet. I have one that I got last year but that does not afford me enough experience to say one way or the other.
John Romano
bunjingi@aol.com
Rhode Island, USA