This should have --enable-gstreamer as a config option now that we have gstreamer 0.8 I think. And it needs recompiling to work with current mono, it appears. I just discovered the staging repo, so I don't know if this is the right thing to do when I have a suggestion.. but here's hoping.
I think --enable-gstreamer is the default, so you don't need to explicitly add it.
I rebuilt the new Muine (0.5.1) against the latest mono and gtk-sharp 0.18. It works fine for me.
It didn't need to be recompiled, gtk-sharp just had to be updated to 0.18. I just realized that was my package, so I'll be uploading it soon.
"Contrary to popular belief, penguins are not the salvation of modern technology. Neither do they throw parties for the urban proletariat."
Btw, muine 0.52 just appeared and works fine with the current pkgbuild (changing the filename/md5 of course).
Edit: Also, the reason I am not convinced gstreamer is default is because I compiled the package from abs and found flac didn't work for some reason - claims to be playing, but time does not tick forward and no sound is made. Recompiling with enable-gstreamer seemed to fix this. It also dumped a xine config in ~/.gnome/muine before I recompiled.