Hi fox
libcamel is part of the evolution-data-server package and it is listed as a dependency for rhythmbox.
rbistolfi@vector [ ~ ] %grep -r libcamel-1.2.so.11 /var/log/packages
/var/log/packages/evolution-data-server-2.22.1.1-i586-1gsb:usr/lib/libcamel-1.2.so.11.0.0
rbistolfi@vector [ ~ ] %slapt-get --search --show rhythmbox | grep Required
Package Required: GConf >= 2.22.0-i586-2gsb,ORBit2 >= 2.14.12-i586-2gsb,aaa_base >= 12.1.0-noarch-2 | glibc-solibs >= 2.7-i486-10,alsa-lib >= 1.0.18-i586-1vl60,atk >= 1.22.0-i486-1,audiofile >= 0.2.6-i486-2,avahi >= 0.6.22-i586-3gsb,cairo >= 1.6.4-i586-1vl60,cxxlibs >= 6.0.9-i486-1 | gcc-g++ >= 4.2.3-i486-1,db44 >= 4.4.20-i486-2,dbus >= 1.1.20-i486-1,dbus-glib >= 0.74-i486-2,e2fsprogs >= 1.40.8-i486-1,esound >= 0.2.38-i486-1,evolution-data-server >= 2.22.1.1-i586-1gsb,expat >= 2.0.1-i486-1,fontconfig >= 2.4.2-i486-2,freetype >= 2.3.7-i586-1vl60,gail >= 1.22.1-i586-1gsb,gcc >= 4.2.3-i486-1,glib2 >= 2.16.3-i586-1gsb,gnome-keyring >= 2.22.1-i586-1gsb,gnome-media >= 2.22.0-i586-3gsb,gnome-vfs >= 2.22.0-i586-2gsb,gnutls >= 2.2.5-i486-1_slack12.1,nss >= 3.11.9-i586-2gsb,gst-plugins-base >= 0.10.19-i586-1gsb,gstreamer >= 0.10.20-i586-1vl60,gtk+2 >= 2.12.9-i486-1,hal >= 0.5.10-i486-2,heimdal-libraries >= 1.1-i586-2gsb,libICE >= 1.0.4-i486-1,libSM >= 1.0.3-i486-1,libX11 >= 1.1.4-i486-1,libXau >= 1.0.3-i486-1,libXcomposite >= 0.4.0-i486-1,libXcursor >= 1.1.9-i486-1,libXdamage >= 1.1.1-i486-1,libXdmcp >= 1.0.2-i486-1,libXext >= 1.0.4-i486-1,libXfixes >= 4.0.3-i486-1,libXi >= 1.1.3-i486-1,libXinerama >= 1.0.3-i486-1,libXrandr >= 1.2.2-i486-1,libXrender >= 0.9.4-i486-1,libart_lgpl >= 2.3.20-i486-1,libbonobo >= 2.22.0-i586-2gsb,libbonoboui >= 2.22.0-i586-2gsb,libgcrypt >= 1.4.0-i486-2,libglade >= 2.6.2-i486-2 | libglade >= 2.6.2-i586-1gsb,libgnome >= 2.22.0-i586-2gsb,libgnomecanvas >= 2.20.1.1-i586-2gsb,libgnomeui >= 2.22.1-i586-1gsb,libgpg-error >= 1.6-i486-3,libjpeg >= 6b-i486-5,libmusicbrainz >= 2.1.5-i586-1gsb,libnotify >= 0.4.4-i586-2gsb,libpng >= 1.2.29-i586-1vl60,libsexy >= 0.1.11-i586-2gsb,libsoup >= 2.4.1-i586-1gsb,libusb >= 0.1.12-i486-2,libxcb >= 1.0-i486-2,libxml2 >= 2.6.31-i486-2,nautilus-cd-burner >= 2.22.1-i586-1gsb,openssl >= 0.9.8h-i486-1_slack12.1 | openssl-solibs >= 0.9.8h-i486-1_slack12.1,pango >= 1.20.0-i486-1,pixman >= 0.10.0-i486-4,popt >= 1.7-i486-2,python >= 2.5.2-i486-1,rhythmbox >= 0.11.5-i586-4gsb,totem-pl-parser >= 2.22.2-i586-1gsb,zlib >= 1.2.3-i486-2
I just installed it and slapt-get pulled from the needed deps. Not sure why it didn't work for you. Check your Gslapt configuration and be sure you have the proper SOURCES enabled, you may find some clue in the system logs, specially /var/log/packages and /var/log/pkgtools.
You could try a reinstall for rhythmbox or simply installing the missing dep.
HTH