I'm going to ignore conspiracy theories and keep this short.
Basically, between the spammers, the DDoS attacks, and the relentless ads shown to nonmembers, I think it's time to leave. LJ is like a warm bath that is gradually cooling down. It's no longer pleasant or comfortable, but the anticipated brief pain of getting out to go somewhere better has been enough pain to keep me in. It's hard to completely kill a community, even an online one. There's always a small number of dedicated residents who will let things get really bad before they even think of moving. (See the This American Life episode on the unreasonable persistence of cities)
I've had a good ~5 years here, and especially enjoyed using it during my travels in 2009. The level of detail and richness I shared would not have been possible on Facebook.
No other web service seems to match the combination of depth, multiple privacy settings, and social that LJ does. Google+ comes close but is not good for detailed multimedia posts. Re: Dreamwidth, I am concerned that it does not have enough resources to stay current with evolving web publishing standards. Facebook and Twitter are way too short and ephemeral and have limited privacy controls.
I plan on mainly being active on google+ for short posts and a a not-yet-set-up wordpress blog for longer ones. I realize that Google+'s pseudonym policy is preventing people from using it, but I have a feeling they are likely to give in on that one soon. For the blog I'm debating between using the wordpress.com web service on my own domain and doing my own wordpress installation. I'll do one more post here to note my blog's new location.
Find me on Facebook here: http://www.facebook.com/thismattbell
Find my main web presence here: http://mattishere.wordpress.com/
See you all somewhere else on the giant tapestry of online social interaction. May we meet again.