1. Someone writes a perfectly good functional app, happens to be written in mono, because thats either the authors preferred language or just that he's most familiar/confident with
2. You see all kinds of ridiculous comments such as "Ohh, nice program, too bad its written in mono, wouldn't touch it with a 10 foot poll". or "OMG THIS IS MONO GARBAGE!!!"
there's no reason to treat FOSS developers like this just because of their language/framework choice. Mono apps integrate fine with gnome, and there's nothing hugely wrong with it. I understand there are valid potential concerns regarding patents and non-ECMA parts of mono, but there's no reason for the kind of trolling we constantly see.