Accounts with zero posts, the default layout, and a huge number of communities joined are, well, very often spam accounts and will not be approved. If you are a real person however, and feel you have been denied membership in error, just send me a private message, or make some posts in your journal (they don't need to be public, just show us that you are actually human), or comment on other people's journals or communities.
If a spammer does make it through, please send a private message to myself with a link to the spam in question and I will delete it as soon as I am able (though LJ may nuke it before I do).
Have a happy everyone :)
EDIT: aaaand we keep getting spam in THIS thread, so I will lock it and hope that they move on.