Pressure systems defiantly effect the bite in my opinion, but how much it will effects the bite depends on the severity of the change in pressure, how long the pressure has held in that pattern, and the species your after, however I've found a safe bet is fishing before the storm or as the storm is starting is hot, average pressure the fishing is good, extremely high pressure and extended low pressure systems the bite turns off, you can't argue when you fish a brown spot through the ice one day and manage 5-6 flags and fish the same spot 3 days latter on the start of a low pressure system and land 20 trout, all of which are gorging on anything and everything