I use my 50mm as an all-purpose, everyday lens. It's often the lens I leave on my camera. I use it for some portraits (though mostly use the 85mm for individuals), especially if I want an environmental portrait or if I have more than one person in the photo. For about the last year, it's been the widest angle lens I have! (Finally got the 24-70 f.2.8 though….)
I have lots of bath time portraits of my little one taken with my 50mm (and we do NOT have a big bathroom, ha ha!).
Since you've been used to having a zoom, it may take you some time to get used to having to zoom with your feet. You may even feel limited for awhile, but don't get discouraged because you can do great things with this lens--I'm guessing it's faster than the 18-200 you've been using. You will love the shallow depth of field that you probably couldn't get with your other lens, and the low light capabilities are fantastic. (Low light shooting was probably why I initially bought a 50mm.)