I too am attempting to run Rawr using Crossover with Mono. I am able to run Rawr b10 and B11 but starting with b12 I run into issues.
• Configuration
Mac OS X 10.5.2/CrossOver 6.2.1 (default win2000 Bottle)/Mono 1.2.6 for Windows/Rawr B12.1
• Steps to Reproduce
1. Launch CrossOver.
2. Choose "Install Software..." from the "Configure" menu. Install Mono 1.2.6 for Windows..
3. Once installation completes, launch Rawr b12.1 by double-clicking it in the Finder.
• Results
Issue #1
The Rawr splash screen shows up and an error dialogue is presented which reads, " The current BuffCache.xml file was made with a previous version of Rawr, which is incompatible with the current version. It will be replaced with buff data included in the current version."
Click OK. Then...
Issue #2
The app never seems to fully launch. I see "Rawr: Loading, Please Wait" in the task manager. Further, the following is output to the console:

3/10/08 3:14:50 PM CrossOver[15603] Task error output:
Unhandled Exception: System.ArgumentException: parameters
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000]
at System.Reflection.MonoProperty.SetValue (System.Object obj, System.Object value, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] index, System.Globalization.CultureInfo culture) [0x00000]
at System.Reflection.PropertyInfo.SetValue (System.Object obj, System.Object value, System.Object[] index) [0x00000]
at System.Xml.Serialization.XmlTypeMapMember.SetValue (System.Object ob, System.Object value) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.SetMemberValue (System.Xml.Serialization.XmlTypeMapMember member, System.Object ob, System.Object value, Boolean isValueList) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.SetMemberValueFromAttr (System.Xml.Serialization.XmlTypeMapMember member, System.Object ob, System.Object value, Boolean isValueList) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadMembers (System.Xml.Serialization.ClassMap map, System.Object ob, Boolean isValueList, Boolean readByOrder) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadClassInstanceMembers (System.Xml.Serialization.XmlTypeMapping typeMap, System.Object ob) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadClassInstance (System.Xml.Serialization.XmlTypeMapping typeMap, Boolean isNullable, Boolean checkType) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadObject (System.Xml.Serialization.XmlTypeMapping typeMap, Boolean isNullable, Boolean checkType) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadObjectElement (System.Xml.Serialization.XmlTypeMapElementInfo elem) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadMembers (System.Xml.Serialization.ClassMap map, System.Object ob, Boolean isValueList, Boolean readByOrder) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadClassInstanceMembers (System.Xml.Serialization.XmlTypeMapping typeMap, System.Object ob) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadClassInstance (System.Xml.Serialization.XmlTypeMapping typeMap, Boolean isNullable, Boolean checkType) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadObject (System.Xml.Serialization.XmlTypeMapping typeMap, Boolean isNullable, Boolean checkType) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadObjectElement (System.Xml.Serialization.XmlTypeMapElementInfo elem) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadListElement (System.Xml.Serialization.XmlTypeMapping typeMap, Boolean isNullable, System.Object list, Boolean canCreateInstance) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadObject (System.Xml.Serialization.XmlTypeMapping typeMap, Boolean isNullable, Boolean checkType) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadRoot (System.Xml.Serialization.XmlTypeMapping rootMap) [0x00000]
at System.Xml.Serialization.XmlSerializationReaderInterpreter.ReadRoot () [0x00000]
at System.Xml.Serialization.XmlSerializer.Deserialize (System.Xml.Serialization.XmlSerializationReader reader) [0x00000]
• Notes
1. This is a clean install of CrossOver using the default windows 2000 bottle set up when installing an app for the first time.
2. Issue #1 occurs on b12 and b12.1. With b12, Rawr never launches as with b12.1 but I didn't see anything in the console.
3. I tried using a Windows XP bottle but Rawr failed to launch completely. I found the following in the console even though mono was in fact installed:
3/10/08 2:35:32 PM CrossOver[15603] Task error output: install the Windows version of Mono to run .NET executables
4. I tried deleting BuffCache.xml manually before launching Rawr b12.1 but it still fails to launch.
I sure hope I can get it working on OS X somehow since I am primarily a Mac user and don't have access to windows except when I am at home. Has anyone been able to use b12.1 on OS X in any way (aside from in Windows via Fusion or Parallels)?
Also if I may, let me just say thank you so much for making Rawr. It is really awesome. I've got it on my windows machine and have been using it for a few months now. It has been really helpful! I've recommended it to all the druids I know and a few of them are using it often now. When the cat model was added it helped one of the druids in my guild up his DPS by quite a bit. And I know several people that will be very excited to see that other classes and specs are on the way. A big thank you to everyone who's working on it, and keep up the good work!