I went through lj_releases back to April of last year to look at some of the changes, because I know there have in fact been a ton.

LiveJournal has implemented the long-awaited a la carte icons, not without some bobbles. (Dreamwidth has no plans for same.)
LiveJournal has new site-integrated chat.
LiveJournal has started putting up different user-submitted banners.
LiveJournal has been using interesting different user-heads (remember the Santa hats? Those were really fun. I wrote to Nokia to give them love.)
LiveJournal and Dreamwidth both re-organized navigation based on sanity; Dreamwidth's involved a many-user card sort.
LiveJournal has a new Mobile page (with some things not working as planned); Dreamwidth has a new mobile developer, and you're looking at his lovely #1 beta tester. (Feel my utter overjoy.)
LiveJournal changed tag selection interface, which I actually like quite a bit; not everyone feels the love as much as I do.
LiveJournal separated email and inbox notifications for ESN subscriptions except for PMs. WOO FUCKING HOO!!!!!!!!! (Currently available only as "the horrible hack" on Dreamwidth.)
Both LiveJournal and Dreamwidth legitimized "the magic subscription" (maintainers/admins can get notified for any comment anywhere in their community). (There was previously a browser hack that would force the subscription, since there was a hook for it.)
LiveJournal redid the subscription listing page some, and AJAX saves the day once again, you can kill a subscription without a whole page reload. (Not sure if Dw does that yet.) It doesn't fail back to checkboxes yet, I believe, though.
LiveJournal has internal journal statistics, and My Guests.
LiveJournal has some anti-spam features, like separate settings for comments and entries with links.
LiveJournal made it possible to remove the first-validated email address on an account \o/ omfg we've wanted this FOR FUCKING EVER THANK FUCK
LiveJournal has 'ban everywhere', if you maintain more than one comm and want a certain jackass banned from all of them.
LiveJournal has "notes" for users; in the immortal words of djdance, "I want to describe it shortly."
LiveJournal has better geolocation features now, featuring, um, I wrote the faq, I should know this, and Google Gears, and somebody else in certain Cyrillic territories.
Both LiveJournal and Dreamwidth have made some RTE upgrades.
LiveJournal updates the entry time to the current time unless the time is manually edited or opened to manually edit; Dreamwidth has a button to update the entry time to the current time.
LiveJournal has further restricted the allowed activities of accounts with unvalidated email addresses to fight spam.
LiveJournal has made various & sundry improvements to Writer's Block.
LiveJournal has made various increases to limits.
LiveJournal got hit by a crossdomain scripting exploit, and got a patch to fix the hell out of it in very quick timing. V. impressed.
Both sites have tagging permission upgrades, finer-grained. (Both sites do allow custom groups in comms to edit tags, you just have to create the custom group first.)
LiveJournal lists the number of comments to the entry on the entry itself; Dreamwidth shows it in an image when crossposting.
LiveJournal upgraded its Jabber server.
LiveJournal upgraded little details on polls.
Dreamwidth patched an absolute positioning in comments exploit, and LJ also took this up.
LiveJournal had pingbacks enabled for a while.
LiveJournal has an option to delete all comments by a certain user in an entry (useful for spammers).
LiveJournal community maintainers can cancel outstanding invitations.