Honestly, I didn't try to install MeeGo yet, because there are no proprietary drivers in the image(right now people have to compile their own images), so things like GSM, 3G, camera are not working. But I will definitely try it when nokia releases the image.
About Fedora, you can install it but you will only see the black console. Mer, I didn't try and Neopwn you can't get it right now, unless you buy their flash card with preinstalled neopwn.
There are other bootloaders too, but yea. Also, you system needs to be modified for n900. So, you can't just download armel linux and boot it.
You need to copy kernel binaries, and do other stuff to make it work.