Still matters, but overall awareness of power prioritization is increasing. Back in the day, almost no one knew anything, and people with sound power priorities were a rarity, but now it's probably the exception rather than the rule...at least for anyone who hangs around Open intentionally.
Indeed, I ran into someone with bad power priorities earlier today and was so surprised they stopped moving that I thought they disconnected on me for a second...nope, PP malfunction.
Anyway, if you drop a PP to zero integrity, they fall to 20% output, then stabilize at 50% output after five seconds. Each hit after this has a chance to pop the ship all together, but with slow cycling weapons like rails and cannon it can often take a while to prompt this.