I dont think Ive ever ran into a situation needing a back up phone. Any phone issues Ive ever had were usually same day switches. I plan on trading mine in for a Photon. Im tired of the HTC sense crashes and other bugs since Gingerbread came out.
I'm in the opposite boat as you. Ever since I flashed cyanogenmod I just can't get rid of my EVO. It's like a new phone with hundreds of new features. The battery life and stability are superior compared to stock by far, and I want to keep my EVO until a newer device comes out with full cyanogenmod support.