I've already been doing this sort of cross-platform programming for years with wxWidgets/wxPython. I'm not waiting on Mac support - I'm already using it (and improving it!). What amazes me is that the authors act like Mono is breaking new ground by having a portable programming language that can do GUIs but is easier than Java. Hello? Apparently no one ever told them about Python/wxPython?

The advantage I see is allowing .NET developers to easily develop for linux. It may be a while (or forever) before many Windows development companies decide its valuable to go cross platform in order to support linux, but if they can immediately transfer .NET skills to linux development the barriers are definitely lowered.

Call it a deal with the devil, but if people can use the same applications under linux that they would under windows thats one less reason not to switch.