Thanks to suricattus, from whom I now quote, because she said it better than I would anyhow:
For me, LJ is my coffee break, my social hour, my connection into a community that amuses, entertains, educates and occasionally infuriates me. In other words, it feeds my brain, the very thing I need to write. Reruns of CSI, and the eternal siren call of the nap are far more deadly to my productivity than an LJ-run.
Mileage varies, and assuming Your Experience is the professional boiling point for all writers is pretty egotistical(which is why all the best career advice to writers can pretty much boil down to 'this is what I found, find what works for you.'
What she said, except for me it's more likely to be Law & Order: Criminal Intent reruns. *laughs*
Edited to add: Oh, look, pnh weighs in also:
I dunno, call me crazy, but it seems to me possible that for some writers, blogging is a time sink and a creative drain, while for others it's a source of connection, energy, and inspiration. It might even be that human beings, not just writers, are all different from one another. I realize that this reveals me as prone to wild, nutty speculation, but that's probably why I work with that crazy rocketship stuff.