I like Mono; as a .NET developer it gives me another option to deploy my apps to, and it's versitility means it finds life in places that Microsoft's .NET stack will never go (things like Wii or the iPhone).
Really, there isn't a problem with "widespread concerns about Mono", there's a core group of morons from the Boycott-Novell crowd who are paranoid and misinformed trying to get rid of something for what is essentially software religious reasons. Most of
these people aren't even devs, they're just users who are trying to tell devs who give up their free time to work on OSS how to work.
This post summarizes pretty well why all the anti-mono stuff is just astroturfing on the part of what is really a very small group of crazies:
http://www2.apebox.org/wordpress/rants/124/ (edit: didn't realize this same thing was linked in the first post)