First, an addition to "How can I help?":
You can help beta-test new features or functions before they are implemented on the main site. For this purpose, LiveJournal maintains an external server (http://test.livejournal.org/) that is separate from LiveJournal. If you wish to help testing, watch the lj_test community (http://www.livejournal.com/userinfo.bml?user=lj_test). Whenever new features are brought to the test server, an entry will be posted in lj_test; then you can test this new feature, and if you find problems, comment on the entry in lj_test.
Next, perhaps a new FAQ. ruakh has already posted about the "!" thing you can add to your username while logging in. Well, I was wondering, maybe we should create a little FAQ now to collect several of these little things in future. Maybe something like, What are some lesser-used "hidden" features??
Searching for a username in the "Search" box at the top of all system pages will lead you to the User Information page (http://www.livejournal.com/userinfo.bml) for the user. However, it is possible to append the text "/pics" to the username, and you will be redirected to the User Pictures page (http://www.livejournal.com/allpics.bml) instead. For example, if you enter "exampleusername/pics", you will be taken to http://www.livejournal.com/allpics.bml?user=exampleusername.
In the login boxes that appear at the top of system pages while you are not logged in, it is possible to append an exclamation mark ("!") to your username, and this will set the Expiration option to "Never". Additionally, you can append a less-than character ("<") to change the "Bind to IP address" option to "Yes".