I changed glib so it doesn't load system gio modules. Can you try this update?
http://www.libsdl.org/tmp/steam-runtime-update-2.sh
http://www.libsdl.org/tmp/steam-runtime-update-2.tar.gz

I tried running the .sh, same error. Just in case, I also tried deleting and uncompressing manually (I took a look inside the script), still nothing.

Okay, I know what's going on, and this should be fixed in the next update.
My theory is that if you do this:
STEAM_RUNTIME=$HOME/.steam/root/ubuntu12_32/steam-runtime steam
it will work, with the new libs.

@slouken nope even with that last command, still the same error

Interesting.
Can you show the output of this:
md5sum $HOME/.steam/root/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libgio-2.0.so.0
grep STEAM_RUNTIME $HOME/.steam/root/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libgio-2.0.so.0

Then can you do this and attach the output of /tmp/steam-strace.txt
STEAM_RUNTIME=$HOME/.steam/root/ubuntu12_32/steam-runtime strace -f steam 2>&1 | tee /tmp/steam-strace.txt

Thanks!

2927837e55d6d2e9bf6d6c2efed07933 /home/neven/.steam/root/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libgio-2.0.so.0
no output on second grep cmd

Cant upload txt files only images, just replace extension with .txt :)

I don't think we have the same bug, @nevenblazic, 'cause STEAM_RUNTIME=$HOME/.steam/root/ubuntu12_32/steam-runtime steam fixed it for me. I have Steam running right now.

Yeah maybe you are right, but i think error msg was same, i did that cmd just now again and saw steam updater pop up for ~2sec and again failed , this is the output
$ STEAM_RUNTIME=$HOME/.steam/root/ubuntu12_32/steam-runtime steam
Running Steam on ubuntu 13.04
STEAM_RUNTIME has been set by the user to: /home/neven/.steam/root/ubuntu12_32/steam-runtime
Installing breakpad exception handler for appid(steam)/version(1359765526_client)
Looks like steam didn't shutdown cleanly, scheduling immediate update check
Installing breakpad exception handler for appid(steam)/version(1359765526_client)
Installing breakpad exception handler for appid(steam)/version(1359765526_client)
unlinked 0 orphaned pipes
removing stale semaphore last operated on by process 11952 with name 0eBlobRegistryMutex_69E3DEB518D781461B99B63FD0539087
removing stale semaphore last operated on by process 11952 with name 0eBlobRegistrySignal_69E3DEB518D781461B99B63FD0539087
removing stale semaphore last operated on by process 11952 with name 0emSteamEngineInstance
removing stale semaphore last operated on by process 11952 with name 0eSteamEngineLock
/home/neven/.local/share/Steam/ubuntu12_32/steam: symbol lookup error: /usr/lib/i386-linux-gnu/gio/modules/libdconfsettings.so: undefined symbol: g_mapped_file_get_bytes

Just to be on the safe side, did you download the .tar.gz and run the .sh he provided earlier?

My fault, i did see you comment after those 2 links saying that its not working again, and i forget to try it.. dl it now

With those 2 files update and STEAM_RUNTIME=$HOME/.steam/root/ubuntu12_32/steam-runtime steam its working

So @slouken was right, and this should be fixed in the next update. I guess this can be safely closed, but I'll let him be the judge of that :P