Suggestion: Have a customised area on the left-hand navigation bar where people can add their own links.
In Depth: Users will be able to add their own links to the navigation bar on the left so they can link to communities, pages, resources, other sites, whatever. This idea struck me when duchess_webb said she used the links mainly as a reference. This idea also expands on goldrose's suggestion.
Suggestion for Implementation: All users could get 3 slots, paid users get 10, and perm accounts get 15 (like user pics). Another incentive to get a paid account, perhaps.
Problems: Data would have to be stored on the LJ database, since cookies suck. Other styles (?setscheme=) will either have to be updated or unsupported. New code will need to be written, since I don't think anything similar is implemented elsewhere.
Good Things: It would be very handy to have custom links to communities you read but aren't listed on your friends list. It would be handy for "copy link address" stuff for reference.