Kay, everyone seems to be missing a few key features, so time to list a few as I recall them. Certain entries are strongly recommended for most users.
UserCP Tips:
*Signatures can upload images for a controlled signature method (but not available)
*Do not attempt to upload an avatar from the web. No matter how you try to set an avatar, the site uploads the data locally. This means that often the best way to set an avatar is to upload from your own computer.
*Many people like using vCards for building social communication (under options). This and filling one's profile with IM names is often useful to such ends.
*Thread subscription occurs by default, but without email notifications. Check your UserCP for a list of all subscriptions. If you want to reduce the account maintenance required for this, it is best to disable this feature (under options).
*Recommend setting "Show New Private Message Notification Pop-up" for ALL members (options). This setting gives an automatic alert notification when you receive a new PM, and is strongly recommended as a highly useful feature. The pop up is only a system alert box, so it harms nothing.
*Thread display settings can be customized (options). Try finding the right setting for you, you might be surprised how useful the other settings can be (just do not select "Linear - newest first").
*Unless you can not handle it, always set the "Message Editor Interface" (options) to Standard Editor (not default). This setting gives a much more powerful interface. Eventually we might get the other option implemented (which I often call 'wisiwig' due to how hard it is to say) which is even more powerful, but too powerful for some.
Calendar and Events
*The calander by default lists birthdays, but is powerful enough to list various other special events. Tor could use this feature to list special events which occur, so checking it often could be quite useful.
*Special events are listed in your UserCP under "Event Reminders" and on the day of are also listed at the bottom of the main page. Remember that this is not only birthdays.
Searching
*"New Posts" are still the fastest way to stay up-to-date with recent posts, and
vB uses a few added features to make it more effective. If you like keeping up with posts, try this feature (also is "Today's Posts" for an alternative).
*"Who's online" is located under Quick Links, which should otherwise be self explanatory, but is still powerful. It isn't as significant as my days Rping, but it is there if you want to know if there is anyone active.
*Member searches are much more powerful. Using the advanced search, you could do something such as ask it to list all users playing on a certain server. This lets you find others who are on your own server.
*Post searches can use highly detailed arguments for searches, to find things in any detail. As usual, searching for information is preferred before making a new topic about it, so that there aren't so many reoccurring topics.
Threads and Topics
*In each section, they are sorted by pre-defined arguments. The area at the bottom of the thread list shows the Sort Type (normally post time) and timespan (how far back to list posts). The first lets you post based on a variety of criteria (such as hot topics), and the second will restrain people automatically from necros of old topics. Make sure to keep these settings sensible to your own purposes. You can also do sorting from the table headers.
*You can also auto-subscribe to your favorite forums. The option is listed under "Forum Tools".
*To go to the last unread post in a thread, click the

button. To go to the last post, click the

button.
*Always keep track of new Announcements and Stickies. They are automatically separated for your own usage.
*Always track markings on threads, such as subscriptions. They let you know which threads aren't normal threads. Hovering over the icon on the far left tells you how much you contributed to the thread (if at all).
*Hovering over a topic bar gives you an initial quotation of the first post. This works in various locations, and is useful to know what kind of discussion is being referred to.
Posting
*For each reply, there is simple-to-use options, and not just the quote button. Multi-quote makes it much easier to quote a chain of people, and the Quick Reply Button is required to enable the box at the bottom of the thread to make a reply (to quote, check the quote box in the quick reply area).
*Edits and Quick Replies occur as pre-generated pages, so they load much faster then an advanced edit. Stick to them when possible.
More details as they come up.