With the latest Unity3d 3.4 update they have set MonoDevelop as default. I’m going to give it a try and compare how the experience is working with mono develop compared to my usual textmate. One thing the compels me is the Intellisence which might come in handy and save me a lot of unity reference lookups to see what the right types are for the method call. Though before I could start using Mono Develop I had to get rid of the whiteness ! As mono develop uses GTK+ you should be able to just drop in a gtk theme and be fine. Alas it was not as easy as this 
You can download some dark themes I found including my howto in one package here : http://dl.dropbox.com/u/1723477/darkmono.zip
After some experimenting I found something that works fairly well for me. Follow along if you are interested 😀
Download a GTK+ theme to your liking. You can use sites like : http://gnome-look.org/
Make a new directory in your homedir called .themes : mkdir ~/.themes
Extract your downloaded themes to this directory.
After that you :
– Start Mono develop
– select visual style -> Interface theme -> clear looks black blue
– select text editor -> syntax highlighting -> irBlack
– Quit Mono develop
Then either backup or remove this directory and file
mkdir ~/default_monotheme sudo mv /Applications/Unity/MonoDevelop.app/Contents/Frameworks/Mono.framework/Versions/2.6.7/share/themes/ ~/default_monotheme mv /Applications/Unity/MonoDevelop.app/Contents/Frameworks/Mono.framework/Versions/2.6.7/etc/gtk-2.0/gtkrc ~/default_monotheme
Then start mono develop again, and now your eyes are at ease 🙂
Happy coding everyone !
Code Noctis 