My hub makes fun of the amount of online social networks I'm a part of...twitter, facebook, flickr, etc...but they each serve a different purpose and I try to keep it reasonable and limit the number of sites I join. However, I have recently fallen in love with tumblr. 
I'm constantly bookmarking sites or saving blog posts in my google reader--but I'm such a visual person that when an image catches my eye online I want to snatch it up (I compare it to ripping out magazine pages--the old fashion way). Tumblr does just that and even creates a link back to the original source...magic!
Above is an archive of all the posts I've made so far.
This may be old news to some of you guys -- but I am in love. It's acts as my virtual pin-up board for inspiration. If you currently blog on tumblr, do you have feedback on how you use it?