I remember using Qt for a C++ project I made a few years ago, and rather liked Qt particularly for how nice the application looked without requiring much extra work for cross-platform work, other than recompiling for Mac, Linux, and Windows. (Of course there's the binary packaging issue on each of the platforms also.).
I've looked at Qyoto (hmm no binary that looks like it works for Leapord, and it needs to use SMOKE), and qt4dotnet (last release July 2010, looks like it needs Qt jambi), and Qt# (seems extinct).
What are some good tutorials, or links to get me started on using Qt with MonoDevelop / C#?
Not the actual answer, but I wouldn't recommend using Mono with any UI library. IHMO, for some server/console stuff Mono is OK, but not for UI.
I participated a project, which used Mono first with WinForms (which were very badly implemented on Linux) then with GTK. The idea of portability didn't pay off. You fill pretty soon bump against platform specific flaws.
I would recommend using Qt with C++. With the way how Qt allows you to minimize use of pointers you could learn the required subset of C++ very quick.
regards.