Of the suggestions received, I do like:
--Limit free user pix to zero or one.
--Don't allow free users to use img tag and/or HTML.
--Limit number of times per day free users can post.
--Limit amount of time per day free users can be logged in.
(I suspect if this could be implemented, it would go the farthest toward handling the overload)
--Limit friend lists of free users.
--Limit community creation to paid users only.
--Allow free users only one journal style, no customizing. But also make sure they can see the extra styles available to paid users.
--Make certain LJ tshirt designs only available to paid members. Create other premiums available only to paid members or people who contribute money or time.
--Auto-subscribe new users to a newsletter or community letting them know about LiveJournal options and encouraging them to get involved and to pay
--Add alternate payment methods
--make paid accounts more desirable: more user icons, image server space
--put a "unpaid/pay here" button on free users' accounts.
--Emphasize the Community aspect of LJ.
--Severely restrict the size of pics posted (I think this should be done for *all* journals, not just free users' journals -- large pix should only be available via links).
--Set LJ up as a non-profit to allow tax deductible contributions
--An icon or notification or something that will indicate a new post on the friends page
--A delay page after posting a new entry or comment
--Create an "only friends can comment" option.
--After creating a new account, a person has to wait for an email before they can post anything.
--Require user to authorize comments in zir journal by new users
--Reduce thoughtless community creation
--Implement an "abuse point" system or a rating system like eBay's
--Create an account to which troublesome users can be reported
--Have anonymous comments turned off by default
--Delete inactive accounts to free up namespace.
I don't like:
--Limiting free users' ability to interact with others (e.g., by limiting the making or receiving of comments, or limiting users from joining communities). REASON: Those go against the community spirit of LJ.
--Limiting free use to a 30 day trial. REASON: Goes against the philosophy of LJ to provide a free service.
--Banner ads. NO NO NO! REASON: Unweening hatred of banner ads.
--Invitation codes. REASON: This would chill interaction among people who don't know each other ("is this person commenting on my journal only to receive an invitation code?") which is one of the treasures of LJ.
--System whereby a person could vote for another person on the basis of their journal content. REASON: Feels too coercive/cliquey to me.
--Comments labeled "free user". REASON: It's one thing to give free users limited functionality in their journals, but it's another thing to brand them when they comment on other people's. journals.
whole thread is here