In Ubuntu Lucid, with the PPA version; I get this stack trace as Docky crashes when I clear recent documents.

$ docky
[Info  11:46:36.393] Docky version: 2.1.0 bzr docky r1332 ppa
[Info  11:46:36.494] Kernel version: 2.6.32.22
[Info  11:46:36.497] CLR version: 2.0.50727.1433
Marshaling changed signal
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: Operation is not valid due to the current state of the object
  at System.Linq.Enumerable.First[FileDockItem] (IEnumerable`1 source) [0x00000] 
  at RecentDocuments.RecentDocumentsItem.UpdateInfo () [0x00000] 
  at RecentDocuments.RecentDocumentsItem.RefreshRecentDocs () [0x00000] 
  at RecentDocuments.RecentDocumentsItem.<RecentDocumentsItem>m__2 (System.Object , System.EventArgs ) [0x00000] 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  --- End of inner exception stack trace ---
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] 
  at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x00000] 
  at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00000] 
  at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] 
  at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x00000] 
  at GLib.SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x00000] 
  at GLib.SignalClosure.MarshalCallback (IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data) [0x00000] 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at GLib.SignalClosure.MarshalCallback(IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data)
   at Gtk.RecentManager.gtk_recent_manager_purge_items(IntPtr , IntPtr ByRef )
   at Gtk.RecentManager.PurgeItems()
   at RecentDocuments.RecentDocumentsItemProvider+<ClearRecent>c__AnonStorey0.<>m__0(System.Object o, Gtk.ResponseArgs args)
   at System.Reflection.MonoMethod.InternalInvoke(System.Object , System.Object[] , System.Exception ByRef )
   at System.Reflection.MonoMethod.Invoke(System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(System.Object obj, System.Object[] parameters)
   at System.Delegate.DynamicInvokeImpl(System.Object[] args)
   at System.MulticastDelegate.DynamicInvokeImpl(System.Object[] args)
   at System.Delegate.DynamicInvoke(System.Object[] args)
   at GLib.Signal.ClosureInvokedCB(System.Object o, GLib.ClosureInvokedArgs args)
   at GLib.SignalClosure.Invoke(GLib.ClosureInvokedArgs args)
   at GLib.SignalClosure.MarshalCallback(IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data)
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at Docky.Docky.Main(System.String[] args)
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose
Cairo.Context: called from finalization thread, programmer is missing a call to Dispose