It has got me a decent amount of work over the last couple of years. The carpet & upholstery page pulled us about 1000 per month, extra work, so free advertising and that's always good. The window page brought work in too, but the sites we used to post on are either too busy now or nearly dead, so we don't bother anymore as we have enough work.
It's handy if your custies are members on your page etc as you can PM them for payment or access. If you want advice about google rankings etc, ask Nathanael Jones. He'll give you good advice. A page with no traffic and full of window cleaners is worthless IMO.
If all it was about was how many likes, I'd be happy. I've got about 350 on my carpet page, about 550 on my window page and about 1400 on my German carpet page. We get quite a bit of work from our websites now and don't really bother with Facebook.
Hope that helps.