Why do I ever bother with Mono? Why? Well I have a belief that large complicated software should be written in an appropriate language. At the moment, that either means a JVM-based language (like Java) or C#. Java doesn't really work on the Desktop (even though I'm a user of Eclipse, Oracle SQL Developer, and many Telco products that are Java desktop apps) as running many, small memory footprint apps for more than a few hours at a time is the desktop experience - and that isn't Java's forte.
On Linux, we have a top quality CLI/CLR implementation and bindings to write desktop apps in Mono. The only problem is, we don't have the tools. :-( Monodevelop is flaky, unstable and let's face it, unusable. Perhaps it's better on (open)SUSE, but 1.0 RC1 on Fedora 9 is, um, crap. Sorry to be so blunt.
Now, it may be because I have some legacy crud in my home dir, but it is confusing, freezes, claims to build solutions when it hasn't, gives cryptic error messages, and is just not ready for prime time. What are add-ins for (I knid of know)? Why are mine "wrong"? What is the correct repo URL? Why don't they update?
For Java, there's Eclipse, Netbeans, and (non-free) Idea all of which are excellent. I've used the Express editions of Visual Studio, and while they're not as good as Eclipse (!) they do the job well. (Another thing: why isn't VS free to download? If you want more decent Windows apps, don't raise the barrier to entry). (Aside: Oracle SQL Developer 1.5 is pretty fantastic for writing PL/SQL. As good as Toad? Well, better than the old, shonky version (7.x?) I had ... obviously it doesn't have Toad's DBA functions, but still. It rocks).
So, the moral is - stop f_cking around writing Moonlight or whatever - fix the development environment.