Tomboy, Gnote, and the limits of forks

If you're smart you can have both performance and high level features. See for instance http://live.gnome.org/Vala (It's classes are even exported to C = available to all). glib constraint is way better than .NET and virtual machine constraint.

"security"
BS. More dependencies = more to attack

"speed of development"
BS. You'll have to solve the same fundamental problems in each language. High level abstractions can and are being made everywhere. The high level platform may look fancy at the beginning, but in the end it only enforces restrictions on you and your "spped of development" deteriorates. If you choose a high level platform, make sure it at least have seemless integration with C [like Python].

"portability"
BS. Mono apps is portable to .NET platforms only?

"richness of libraries"
Compared to what?