Not always. Some clients have invested heavily into .NET components and/or libraries. And when that happens, you like to have an option or two and in some cases, Mono was a good enough choice.

True story... once I inherited a project that banked on a closed source C# *.dll at the center of their process that they wanted me to wrap with some Mono .NET web services that would hit this *.dll and spit out their values that were embedded in that damn *.dll. Had to write something that would accomplish this for those cheapskates until they either got the source for that *.dll or they figured out the 7+ years of research into the algorithms (which SHOULD HAVE been in the goddamn database) using Mono... ugh.

And no. I was not (at that time) a .NET dev. But I can program - it's all just syntax. The rest is just being a petty ****er about what pays the bills.