I've heard different definitions for floating nets, I wonder which type you are trying to find. Here are a few definitions I've heard in the past:
1) nets that connect to only one device
2) nets that don't connect to any devices
3) nets connected only to gates of devices without actually being driven by a transistor connected to power or ground
NOTE: If anybody reading this has heard of other definitions please share your comment. Maybe I should try to maintain a list here in this Calibre forum of several known types of floating nets along with ideas for checking each one?