libmono-dev has been removed in mono 2.10. It is replaced by libmono-2.0-dev

Following packages must update their bdeps when mono 2.10 hits unstable:

dd-list $(grep-dctrl -FBuild-Depends -FBuild-Depends-Indep libmono-dev -sPackage /var/lib/apt/lists/*Sources | sed -e "s/Package: //"|sort -u)

Mirco Bauer <meebey@debian.org>
   gluezilla (U)
   gnome-desktop-sharp2 (U)
   gnome-sharp2 (U)
   gnome-subtitles (U)
   gtk-sharp2 (U)
   mod-mono (U)
   mono-addins (U)
   mono-debugger (U)
   monodevelop (U)
   monodevelop-vala (U)
   smartirc4net (U)
   webkit-sharp (U)
   xsp (U)

Debian CLI Applications Team <pkg-cli-apps-team@lists.alioth.debian.org>
   blam
   gnome-subtitles
   gshare
   monodevelop
   monodevelop-vala

Debian CLI Libraries Team <pkg-cli-libs-team@lists.alioth.debian.org>
   gnome-desktop-sharp2
   gnome-sharp2
   gsf-sharp
   gtk-sharp2
   log4net
   mono-addins
   ndesk-dbus
   nemerle
   smartirc4net
   taoframework
   webkit-sharp

Debian LibreOffice Maintainers <debian-openoffice@lists.debian.org>
   libreoffice

Debian Mono Group <pkg-mono-group@lists.alioth.debian.org>
   gluezilla
   mod-mono
   mono-debugger
   xsp

Eric Dorland <eric@debian.org>
   lat

Sebastian Dröge <slomo@debian.org>
   gluezilla (U)
   gnome-desktop-sharp2 (U)
   gnome-sharp2 (U)
   gshare (U)
   gtk-sharp2 (U)
   log4net (U)
   mono-addins (U)
   ndesk-dbus (U)
   nemerle (U)
   taoframework (U)

Rene Engelhard <rene@debian.org>
   libreoffice (U)

Evgeni Golov <evgeni@debian.org>
   libindicate (U)

Sam Hocevar <sho@debian.org>
   taoframework (U)

Dylan R. E. Moonfire <debian@mfgames.com>
   log4net (U)
   mod-mono (U)
   taoframework (U)
   xsp (U)

Francesco Namuri <francesco@namuri.it>
   drapes

Carlos Martín Nieto <carlos@cmartin.tk>
   blam (U)

Siegfried-Angel Gevatter Pujals <rainct@ubuntu.com>
   mistelix

Jo Shields <directhex@apebox.org>
   gluezilla (U)
   gnome-desktop-sharp2 (U)
   mod-mono (U)
   monodevelop (U)
   monodevelop-vala (U)
   webkit-sharp (U)
   xsp (U)

Jose Carlos Garcia Sogo <jsogo@debian.org>
   gsf-sharp (U)

The Ayatana Packagers <pkg-ayatana-devel@lists.alioth.debian.org>
   libindicate

Tiago Bortoletto Vaz <tiago@debian.org>
   gnome-subtitles (U)