Lawyers use PACER quite a bit, but it's not because they love it or make money from it (in fact, clients are increasingly rejecting "research" charges). It's just that PACER is often faster, easier, and more certain than using the firm's internal document management system. PACER is set up for litigation - DMSes, while they let you store anything, don't understand what the content is.
Our startup is basically tackling that problem - and one of the side benefits will be dramatically reduced PACER bills. There is no reason firms should ever be looking up their own case documents on PACER, since they get them for free in the first place.