There are many social applications out there, and for some inexplicable reason, I use them all in different ways. Each of them seems naturally inclined towards a different function and/or audience. Here's what I've noticed, correct me if I'm wrong:
Tumblr:
Seems to attract young people. Really young - underage young. How do I know this? All lot of people put their age in their profile. (I'm 17!) It's also incredibly easy to get content from other users. Not so easy to upload your own content, but to reblog from another user? Easy peesy. I say this because it takes two clicks to reblog, and a whole process to post an image you first have to save onto your computer. Tumblr functions best as a self-contained universe. Not so many people put on original content. Most reblog - it's easier, but then you can end up in a virtual loop, seeing the same images over and over again.
What I post: visually intriguing photography, calming interiors, epic landscapes, clever sayings, all while citing sources (Note: this is unusual, a lot of the time, you have no idea of an image's original source. I see this as a bad thing). I basically use this as my virtual inspiration wall and actively look for original content. I try to keep it highbrow (no porn). I do not write anything on Tumblr, because it feels wrong. And it looks ugly, like words aren't meant to go there.
Blogger:
Well, here I am. I write here. Other people's pictures go on Tumblr, but my actual words, my own photographs and my thoughts make their home here. I think it's because I can better control the formatting and like the overall look of it, and I can dig a little bit deeper into a topic. However, blogging is isolated. Blogging is an island. People may find you, but only if they're looking. People on Tumblr are actively looking - even if it's to reblog your photographs to show their followers, at least they're out and about. You can amass followers relatively easily on Tumblr, depending on your interests. Blogger not so much.
Twitter:
Ideally, I see this as an open market information exchange: I upload content I find useful and interesting, along with links to this blog, along with my own photographs. It's a good place to interact with other writers as well, and to gain useful information. Eventually, I hope to promote my own book. But with restraint, of course.
In reality, it's a lot of digging around, like searching through a virtual flea market to see if there are substantive gems to be found. There's a lot of auto-tweets and auto retweets. Hashtags sometimes make communication incomprehensible. But I've found some gems alongside the rough. So that keeps it interesting.
Facebook:
Honestly, I have an account, but I don't ever go on it. I can't even be bothered to complain about it, because I've already complained enough times that I bore myself. If I do something "official" I will probably have to open a Facebook page and start pimping it out to everyone I know to "like" it. I feel sorry for my future self.
Instagram:
I don't use this very often. Some people find Instagram to be the most personal account because it shows pictures from people's daily lives, like little personal vignettes. I know the contents of my daily life. It's boring. Here is what theoretical pictures from my Instagram account would be: an office cubicle (multiple angles), tupperware (not restaurant food), a cheap gym (where I would look bad), and possibly some screenshots from my laptop, where I spend an inordinate amount of time.
Pinterest:
I haven't associated my Pinterest account with this blog, because...to be perfectly honest...this is where I lose all self restraint and am an unabashed consumer whore and virtual chef. It has to go somewhere. On this blog, I made an intentional choice not to talk too often about shopping or fashion or makeup, because I think that adds to consumerism and unhappiness by promoting unrealistic ideals. Well, those choices get thrown into the garbage on Pinterest. It is just too easy to pin things that you want to buy, or pretty things you like to look at, cats - things that range between shallow and embarrassing. I have a recipe for homemade twix on Pinterest, and that's one of the better ones, because twix at least is a food group. Right. We all need a virtual outlet, and although ideally it would be exercise, in reality it is Pinterest.