The main problem is that ED has no HW acceleration for video decoding (and never will have).
I don't know if the stock Maemo kernel fully supports ext4, but I guess most - if not all - ED users use KP anyway.
I think I can clear this up. Do you remember that I had to macgyver a fake Squeeze pulseaudio package that actually contained the Lenny version to stay compatible to Maemo's pulseaudio protocol version? So what you have now is a Lenny pulseaudio with a Squeeze gcompris that thinks it can rely on a Squeeze pulseaudio, which in this case causes trouble. I believe I have a better idea for a new pulseaudio package which actually contains the correct pulseaudio version and is compatible to Maemo. But in order to do that I have to recompile pulseaudio, which I can't do on the N900 due to the watchdog. I already have an armel qemu VM set up but that comes with huge performance penalties (8-10% of the x86 host CPU seems to be reasonable), so I intend to wait with any actual work until Wheezy is frozen, which is scheduled for June. I will then try to create a minimalistic Wheezy image containing the proper (but recompiled) pulseaudio which will be able to run iceweasel 10 too btw. (I already tried to backport iceweasel 10 to Squeeze by reproducing what the people at mozilla.debian.net are doing for i386 and amd64 but gcc4.4 for armel is too buggy for that and I didn't succeed in compiling gcc4.6 on Squeeze armel either, so I finally gave up on that.)