Additional information:

[ignacio@wide pkg]$ find /usr/lib -name libgnome-desktop* 2>/dev/null
/usr/lib/libgnome-desktop-3.so
/usr/lib/libgnome-desktop-3.so.0
/usr/lib/libgnome-desktop-3.so.0.0.8
[ignacio@wide pkg]$

[ignacio@wide ~]$ ldd $(which nautilus)
linux-gate.so.1 => (0xb7775000)
libSM.so.6 => /usr/lib/libSM.so.6 (0xb7740000)
libICE.so.6 => /usr/lib/libICE.so.6 (0xb7729000)
libXrender.so.1 => /usr/lib/libXrender.so.1 (0xb7721000)
libnautilus-extension.so.1 => /usr/lib/libnautilus-extension.so.1 (0xb7718000)
libgnome-desktop-2.so.17 => not found
libunique-1.0.so.0 => /usr/lib/libunique-1.0.so.0 (0xb770c000)
libdbus-glib-1.so.2 => /usr/lib/libdbus-glib-1.so.2 (0xb76eb000)
libpthread.so.0 => /lib/libpthread.so.0 (0xb76d0000)
libgailutil.so.18 => /usr/lib/libgailutil.so.18 (0xb76c8000)
libgtk-x11-2.0.so.0 => /usr/lib/libgtk-x11-2.0.so.0 (0xb726b000)
libgdk-x11-2.0.so.0 => /usr/lib/libgdk-x11-2.0.so.0 (0xb71bd000)
libatk-1.0.so.0 => /usr/lib/libatk-1.0.so.0 (0xb719e000)
libgio-2.0.so.0 => /usr/lib/libgio-2.0.so.0 (0xb7072000)
libgdk_pixbuf-2.0.so.0 => /usr/lib/libgdk_pixbuf-2.0.so.0 (0xb7050000)
libcairo.so.2 => /usr/lib/libcairo.so.2 (0xb6f95000)
libpango-1.0.so.0 => /usr/lib/libpango-1.0.so.0 (0xb6f54000)
libgobject-2.0.so.0 => /usr/lib/libgobject-2.0.so.0 (0xb6f06000)
libgmodule-2.0.so.0 => /usr/lib/libgmodule-2.0.so.0 (0xb6f02000)
libgthread-2.0.so.0 => /usr/lib/libgthread-2.0.so.0 (0xb6efd000)
libgconf-2.so.4 => /usr/lib/libgconf-2.so.4 (0xb6ec3000)
libglib-2.0.so.0 => /usr/lib/libglib-2.0.so.0 (0xb6dd5000)
libxml2.so.2 => /usr/lib/libxml2.so.2 (0xb6cae000)
libX11.so.6 => /usr/lib/libX11.so.6 (0xb6b93000)
libexif.so.12 => /usr/lib/libexif.so.12 (0xb6b5e000)
libexempi.so.3 => /usr/lib/libexempi.so.3 (0xb6a70000)
libm.so.6 => /lib/libm.so.6 (0xb6a45000)
libc.so.6 => /lib/libc.so.6 (0xb68df000)
libuuid.so.1 => /lib/libuuid.so.1 (0xb68db000)
libpangoft2-1.0.so.0 => /usr/lib/libpangoft2-1.0.so.0 (0xb68b4000)
libpangocairo-1.0.so.0 => /usr/lib/libpangocairo-1.0.so.0 (0xb68a9000)
libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0xb6823000)
libfontconfig.so.1 => /usr/lib/libfontconfig.so.1 (0xb67f5000)
librt.so.1 => /lib/librt.so.1 (0xb67ec000)
libpng14.so.14 => /usr/lib/libpng14.so.14 (0xb67c6000)
libdbus-1.so.3 => /usr/lib/libdbus-1.so.3 (0xb6789000)
/lib/ld-linux.so.2 (0xb7776000)
libXext.so.6 => /usr/lib/libXext.so.6 (0xb677a000)
libXinerama.so.1 => /usr/lib/libXinerama.so.1 (0xb6777000)
libXi.so.6 => /usr/lib/libXi.so.6 (0xb676a000)
libXrandr.so.2 => /usr/lib/libXrandr.so.2 (0xb6763000)
libXcursor.so.1 => /usr/lib/libXcursor.so.1 (0xb675a000)
libXcomposite.so.1 => /usr/lib/libXcomposite.so.1 (0xb6756000)
libXdamage.so.1 => /usr/lib/libXdamage.so.1 (0xb6753000)
libXfixes.so.3 => /usr/lib/libXfixes.so.3 (0xb674e000)
libdl.so.2 => /lib/libdl.so.2 (0xb6749000)
libpcre.so.0 => /lib/libpcre.so.0 (0xb670c000)
libresolv.so.2 => /lib/libresolv.so.2 (0xb66f4000)
libz.so.1 => /usr/lib/libz.so.1 (0xb66df000)
libpixman-1.so.0 => /usr/lib/libpixman-1.so.0 (0xb6674000)
libxcb-shm.so.0 => /usr/lib/libxcb-shm.so.0 (0xb6672000)
libxcb-render.so.0 => /usr/lib/libxcb-render.so.0 (0xb666b000)
libxcb.so.1 => /usr/lib/libxcb.so.1 (0xb6652000)
libORBit-2.so.0 => /usr/lib/libORBit-2.so.0 (0xb65ff000)
libexpat.so.1 => /usr/lib/libexpat.so.1 (0xb65d7000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0xb64e9000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0xb64cc000)
libXau.so.6 => /usr/lib/libXau.so.6 (0xb64c8000)
libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0xb64c3000)
[ignacio@wide ~]$

you simply didn't run pacman -Syu

nautilus 3.0.0 is in the gnome-unstable repo, you should enable it ;)

I did both:

[ignacio@wide ~]$ tail -25 /etc/pacman.conf | head -10

[gnome-unstable]
Include = /etc/pacman.d/mirrorlist

[testing]
Include = /etc/pacman.d/mirrorlist

[core]
Include = /etc/pacman.d/mirrorlist

[ignacio@wide ~]$ sudo pacman -Syu
Password:
:: Synchronizing package databases...
gnome-unstable is up to date
testing is up to date
core is up to date
extra 471.3K 47.5K/s 00:00:10 [######################] 100%
community is up to date
:: Starting full system upgrade...
there is nothing to do
[ignacio@wide ~]$

I did this wrong?

it might be from a plugin that nautilus tries to load?

do this and paste the log

LD_DEBUG=files nautilus > log 2>&1

could be possible, I had installed the nautilus-dropbox but after removing it the problem remains :(

Here you have the output of ld debug output (i do not know how to read it)

thank you all

pacman -Qm

pacman -Q nautilus

please paste the /var/log/pacman.log

Found the root of the problem :D

[ignacio@wide ~]$ pacman -Q nautilus
error: package "nautilus" not found

I've been using the damn nautilus-elementary previously :(

Sorry for bother you guys and thank you!