The only big social media that I use are Pinterest and Blogger.
I love blogging. I love finding and reading blogs. I am inspired to knit more. I discover new (to me) books and movies to try. I find more natural beauty options I love the sewing and fashion inspiration. I just really feel that my little curated collection of blogs is so often truly, practically inspirational. Oh, sure I've wasted time on blogs that I don't benefit from, but overall, I think the blog world is worth my time. I think blogging myself is enjoyable, especially since I can schedule, and so I am planning to make more of an effort to grow it into possibly a bit of job.
Pinterest is another love of mine. I did get my account in the extremely early stages during which you had to be invited, but I didn't understand or use it much until it really sprang into life. Then I went crazy. I think that Pinterest is a great search engine and curating site even with the changes I dislike. The blog promotion is a nice side benefit.
Ravelry and Goodreads both have social media capabilities which I may at some point use (or use again), but right now I enjoy them for their main capabilities.