I was toying with the idea of doing a frequency counter project. I would probably use a prescaler, such as the LMX2322. There's numerous PIC-based projects that do this, the prescaler feeds a pin on the PIC that increments a counter, and then the PIC samples and resets that counter at a known interval. By knowing how many events were counted during the interval, you can compute the frequency in hertz. Ideally I'm shooting for something that would work from the low hertz range all the way up to a gigahertz or so.
I've read AN001, and it looks like there are some logic modes that can detect rising or falling edges on an input pin, and then do something with the FRQx and PHSx, but I'm not exactly sure how to put something practical together from this. I was hoping someone had a working example of a pulse-counting configuration.