According to the Live Journal Stats Page there are a total of 832563 users (as of this writing). Of those, only 690077 have ever updated their journals. That means there are 142,486 live journal accounts that someone started and never even used once.
Now this doesn't include those that have one or two initial entries. There is no real record of such journals but only 307692 livejournals have been updated in the past month. This means that 524871 journals (about 63%) are pretty much dead. Certainly there are some who just don't update more than once a month, but there are statistically far more who have updated in the past month who will never update again. So that number, 524871 dead journals, is probably pretty accurate.
I sometimes wonder about some of these dead accounts. Occasionally I stumble across an account that seemed to be going strong and suddenly just stopped cold for no apparent reason. It seems logical that, with about 300,000 active journals, a few of these people will exit the planet without notice. It is quite common for LJr's that no one in live journal knows who they are in the real world and no one in the real world knows about their live journal. So if something happens to them their journal just turns into a big question mark.
There have been times that I have simply stopped posting in my journal and my LJ friends just kinda let it go with no comment. If I never posted again I imagine some might wonder but I doubt anyone would bother to investigate.
Then there are the journals that people start and quickly get bored with. Some of these journals have been sitting there for years unused. I strongly suspect that most of the owners don't even remember the passwords so these journals will likely sit unused forever. Some of these journals are a real waste of a good name, like diogenes, or me. Me has been sitting there untouched for three years. Maybe LJ should have some kind of appeal process to deal with such obviously dead journals. Me is never going to use this journal so why not throw the name back into the hat and let someone else have it.
Then there are the suspended journals. Like, God. I get a kick out of that notice, "If you are god, please refer to the FAQ…". It seems a lot of the best names get suspended like life, do_me_baby, and sex. The notice says that, "in order to maintain our users' privacy, LiveJournal.com cannot discuss the reasons for any suspension with anyone except the account's owner." But come on...enquiring minds want to know! How the hell did God manage to get suspended?
There are other accounts that people have deleted that seem to be up for grabs. However, the powers that be seem to keep these journals in limbo for a long time. The notice says that they will purge the journal if it is not undeleted by the owner within 30 days. However, that notice often stays in place on a journal for several months before it is actually purged and deleted. Even then the name is not available for use. The journal is simply left there with a notice that it has been purged and deleted. I haven't yet tracked one of these journals long enough to know what happens next.
Overall it seems that a considerable majority of journals on LJ are stuck in limbo with very little chance of ever coming back to life. While it is obvious that the active accounts will take the most resources, clearly there must be substantial expenses in maintaining over 500,000 dead accounts. If I were running this thing I would at least look into deleting any account that is not updated for over a year.