Tumblr

I like to read blogs. I wish more of my friends had blogs. A couple of years ago it seemed like everybody was using Blogger, but now it seems like Tumblr is the current trend. One question I have about Tumblr: do people ever write anything or just post pictures and videos? Most of the time I see posts with a picture or video and a couple of words below it. Is that just how Tumblr works? I'm not knocking it at all, just wondering. I do my fair share of posting videos and such as well.