App Version: Comix 4.0.4
Machine: Clevo / NEO eLAN Laptop
OS: Ubuntu 10.10
This might just be an isolated case but I've decided to post it as reference.
After installing Comix 4.0.4, it automatically overrides Nautilus File Viewer when opening locations from Places (i.e. Documents, Music, Pictures, Videos, Downloads and even mounted hard disks)
I was able to fix it with Ubuntu Tweak, going to System > File Type Manager and searching for Folder. Comix was associated with opening file folders.
Restored Nautilus File Viewer by locating 'folder' in Ubuntu Tweak (File Type Manager > All > folder) and editing associated application.