You can see the involved changelogs here:
There have been many, many reports of a Best Buy page takeover Flash ad, and I've just managed to confirm this ad's existence myself while using my test plus account at Wednesday 1:35AM Pacific. It has sound, and starts upon page load instead of something user initiated like a click. The top of the video has text that's like "CONTENT SPONSORED BY". This is notable because:
* Unlike previous instances of aggressive ads, I have not yet seen marta or others in that capacity tell people this ad would be taken down. I have not heard of anybody reporting it getting any kind of answer back. Additionally, a support request I've seen come in this morning about "pop-ups with singing and other audio are extremely annoying" ended up becoming private, so I don't know what they were told.
* The run of the ad has lasted for days now, and is still occurring without being taken down. Most other ads doing annoying things like this have been taken down by this time.
* This is no fly by night malwarish crappy video remnant that's slipped through the cracks, but a slick ad campaign by a major company.
All of this suggests that this time, the annoying ad may be running with the sanction of LiveJournal. Posts I've caught about this on Icerocket are strongly encouraging the use of Adblock Plus, making this something of a Pyrrhic ad campaign for LiveJournal.
charmian pointed out this article, Google translated from Dutch, which says that 40% of LJ visits come from the US, and in the US 50% of revenue comes from subscriptions.