I've been trying asp.net mvc on mono and the data annotation throws a not implemented exception, does anyone know when will Mono support this?
According to this page http://www.go-mono.com/status/status.aspx?reference=4.0&profile=4.0&assembly=System.ComponentModel.DataAnnotations, it's almost finished...
If that page is correct, you should go and check out latest Mono source code from their GitHub site and test if your application runs fine.
You don't mention which data annotation(s) you are using, but Mono 2.8 is supposed to have more of them completed than Mono 2.6.7.
Mono 2.8 Preview Build: http://mono.ximian.com/monobuild/preview/download-preview/
The final of Mono 2.8 will likely be out next week.
Your other options are to not use them in your MVC code, or implement the ones you need that Mono does not have. Most of them should be pretty trivial to implement.
If you want to use this functionality now, then copy System.ComponentModel.DataAnnotations.dll (MS.NET version 3.5.0.0) into your bin folder. It needs to be assembly version 3.5.0.0, because version 4.0.0.0 didn't worked for me (even with mono 2.8 from trunk).