For a while now I have been utilizing the digimode waterfall in CW pileups, where the DX station is sending on one frequency and listening on others, i.e. he is working split. I don't have a high-cost rig with double receivers, so my split working is done by listening alternately to VFO A and VFO B.
Here is how I do it:
1. I select VFO A with a 500Hz filter.
2. I adjust the DX station so that it has about the same tone as my own CW tone. I see the DX station on the waterfall at around 700Hz, which is my rig pitch.
3. I set up the VFO B with a little bit broader filter. I personally like 1,8kHz, since it makes you hear and see a broader bandwith. Broader filters make it more difficult to distinguish stations in the crowd.
4. When the DX is listening to calls I skim through the pileup band, just a few seconds at a time, trying to figure out how the pileup crowd works and, more importantly: how the DX station listens. This is where the waterfall is powerful: even though a trained ear can hear the tone differences, the waterfall frequency scale tells in numbers how many hertz up and down there are between the QSOs . Very useful!
5. I try to hit my call to the frequency that I think is most appropriate, according to what I have heard (=seen!).
Note: If the DX appears to listen more or less on random frequencies, I use to listen to the crowd first and then briefly adjust my frequency in a free slot between others... Trained operators can do it by listening, but the waterfall screen makes it easy for anybody! I have found this way to be especially fruitful when working rare DX stations in big pileups.
I have worked many nice stations in big pileups with this method. Yes, this method is the same as in RTTY pileups...as matter of fact, I got the idea from there.