When trying to build graphical interfaces on Linux with Mono, you have lots of choice. If you want maximum portability you can use Windows Forms (which don't look so great on Mono) or Gtk# (way better for multi-platform stuff). Both have a pretty standard look, even if WinForms look native only on Windows and Gtk does so on Gnome, and both work very well for standard desktop apps.
However, when doing more advanced graphics or targeting embedded systems, both fall short: WinForms runs OK on Windows CE (even if it is very limited), while Gtk looks pretty boring and may not be the ideal choice on resource constrained systems. The next multiplatform GUI choices that come to mind are Nokia's Qt or Intel's Clutter. Clutter is still a young project, but both frameworks unfortunately lack some good .NET bindings in essence.
In my case I'm starting to use Qt, through the Qyoto bindings. The latest Ubuntu distro already includes the package, which makes getting started pretty easy — at last if it weren't for the lack of documentation.
Qyoto provides a quite complete mapping of the Qt interface, but unfortunately mantains a lot of the original C++ “smell”: many enumerations are given as simple integers, events (the signal/slot system in Qt) don't rely on .NET events but require you to bind methods to signals by their untyped name. Less of a problem, but still not very pretty: in many points Qyoto doesn't respect the common .NET naming conventions and some Qt methods should really be mapped to properties.
Anyway, these minor criticisms notwithstanding, Qyoto provides a simple and complete way to use Qt's power from C#. Let's take a look to a simple example application.
