I think it's a big deal, but I also think too many people make too big a deal out of it. Like if a firm doesn't come to a campus for OCI, it's impossible for graduates of that school to get a job, or if a firm recruits there, it's only a matter of grades to work for that firm.
It does tell you the level of firm and what region graduates go to year after year. If no firms interview from a certain region, or say no BigLaw firms interview at a school, that's going to be an uphill struggle (sometimes monumental) when trying to get a job at that level or in those regions.