I had one of the old ones before it changed names a few times (it was Microsoft Office User Specialist at that time). I used to have it on my resume for many years, but recently took it off. I can't recall ever getting much comment on it specifically and I'm still getting lots of hits without it now -- but of course, my career has advanced by several years since I put it there.
Having strong knowledge of Office DEFINITELY has improved my chances to get hired. Being an expert within the office has definitely moved me forward once there.
I think the certificate itself is helpful to bolster a burgeoning career, and it certainly can't hurt an established one. Is it necessary? No.
Best of luck!