I've occasionally hit PSK operators working split. Unfortunately, their messages usually just say "up" or "down" rather than "up 5" or "down 10" or something like that. I have yet to actually hear anyone calling them or find their split frequency. Is there any "custom" for how far up or down to split on PSK?
Working split and just saying listening "up" is rude, inconsiderate, and unnecessary. In my opinion any station just saying "up" is a LID and is causing unnecessary QRM, no matter how rare the DX is.
They really should say exactly where up, and pick just one spot. If the pileup is too intense, then they need to refine it further by area or letter instead of just ruining the band for all other operation. Not only is it much faster for a DX station to run people when they do not have to hunt and tune, it makes the rest of the band useful for other people.
I can't think of any good reason to not say some specific listening frequency. This new practice of spreading people out is something that started in the last 20 years or so, and is becoming more common as people become less considerate.