I've read several stablity issues with modmono under high load. The root of the problem is GC and the solution is restarting modmono every n hours, and n should be decreased based on error frequency.
I'm planning to develop a heavy load site with mono (I've .net experience and a little java), and I've fears based on this issues like session interruption, http errors ...
At this starting stage of the project, should I switch to Java/tomcat or trust to mod_mono ?
Regards
Depending on how long developing your site (http://www.mono-project.com/Compacting_GC) might be ready for production. While, googleing found some complaints about stability, many were from 2006. Push comes to shove, if mono/mod_mono fail to live up to stability, you could always deploy from windows/iss.
It's a bit of a calculated risk at this point, but if you run into any issues, I'm sure the mod_mono mailing list would help sort out any issues.