I started out very reluctantly with Twitter, at the strong encouragement of Viking's marketing gurus. At first I didn't get it at all--- my feed was full of self-promoting junk, a lot of it from s-p writers but all sorts, really. Then I figured out how to use lists to categorize people...then I figured out how to find and follow interesting people...then I started interacting with them. I love it. People compare Twitter to a water-cooler, where anyone can talk to anyone. That's pretty accurate, but on Twitter you get to pick the people who share your water cooler.
Then other stuff started to happen. Writers I care about read my books and commented on them. Literary agent Janet Reid, who's not my agent, read A Dangerous Fiction, a thriller about a literary agent being stalked, apparently, by a murderous writer. She live-tweeted her reactions, ending with one in which she's reading in bed under the covers because she's too afraid to peek out. I figure she sold more books for me than my own publisher with that series of tweets. I was asked to do a writers' conference and some book club presentations and a whole bunch of interviews.
In other words, my world got bigger and my reach further. Readership of my blog is ten times what it was pre-Twitter. I'm with the OP--it's a wonderful tool, well worth the admittedly steep learning curve.