Mine: dwbeyer.com (shameless plug...) is a bit of several of the above and something else. I started it initially to track my writing progress. I also started to add reviews and such because writing about writing progress... well, for me doesn't really provide much material.
Ultimately though, I hope it helps establish my "brand" online as a writer. I have it connected to Twitter and Facebook such that when I post to my blog, it cross posts to Facebook and Twitter. I have not done much with Twitter, but with Facebook I have found new steampunk friends (people who would be interested in my genre of writing) and found a number of local events to which I am now participating. In some senses, Facebook has been my gateway into the steampunk community. Being part of that community now I feel that I am building legitimacy, credibility and an audience for my writing. At least, I hope.
Stop by and visit my blog at: dwbeyer.com and friend me on Facebook: https://www.facebook.com/dwbeyer or if you are so inclind: I can be reached directly at email@example.com
I have a blog/website, that mainly features my artwork and the specific process I go through to develop each piece. As happens when I write as well, sometimes I start out with a pretty good idea of where I expect to go, but the writing (or sculpture) takes me somewhere else.
Since you asked, it's at www.camrynforrest.com
I would say it's a "here is what I am thinking" but mainly limited to my artwork, or experience at art shows. So much of my day to day life is not steampunk related, nor art-related, that I have kept those thoughts out of the blog for the most part.
No, I don't use twitter either.
I only joined facebook a few months ago, when an art show in which I was interested mentioned that it was easier for them to do all their artist updates on facebook, so I succumbed. Being towed, not kicking and screaming, but with some heel dragging, into the 21st centry.
But I do use tags in my blogs and that works well -- if someone is searching for what I'm writing about that day. Have not used categories yet, not sure where to start with that. But (for example) if you google "steampunk snowglobes" you'll almost certainly get my blog in the first returns, which is great. And when I mention Tesla (as I use his inventions as starting points for some sculptures), that also gets a tag and much interest in that particular blog. The man still has FANS...