Later 2000s and 3000s cannot have CFW perma-flashed, like 1000s and early 2000s can.
But as mentioned above, if they're at 5.03 or below, you can exploit a flaw in 5.03 in order to temporarily load CFW, until the next shutdown. You get MOST of the benefits of CFW, just with a certain increase in hassle-factor. I think there might be some plugin/compatibility issues, but I could be wrong. Not having a later 2000 or 3000, I never fully bothered to educate myself. Currently, if your uncrack-able 2000 or 3000 is above 5.03, I don't think there's anything you can do.
As for those contemplating ditching CFW in favor of more modern OFW, I do believe there is a better solution for you. But again, this only applies to older 1000s and 2000s. I've not done it yet, as it's too much of a hassle for me (I plan on waiting for CFW 6.00 XYZ). But I'm pretty sure you can set up your PSP to use a Pandora as its primary battery. Some Pandora menus have a "test CFW" option that, if what I've read is correct, can allow you to load a temporary CFW instance from the memory stick, not like what those with newer 2000s and 3000s use today, while retaining an official Sony firmware installed to their PSP's flash. If my understanding is correct, a normal boot up = stock PSP firmware of your choice (6.00 at this point, obviously), whereas using the Pandora's alternate loader, you can run a CFW instance.
It's a bit of a hack, but it seems like a decent compromise until CFW "catches up." Though admittedly, I can't say I know all of the details, myself.
Again, this would only apply to PSPs that can actually be cracked by a Pandora battery.