Another tip on collision detection: there's also a mode on the collisions menu that shows intersections, instead of preventing intersections. The main drawback of collision detection is its resource use, if you have a somewhat more complex scene, using collision detection will slow the system down to a crawl. The "show collisions" option seems to be a little less resource intensive, and it also doesn't suffer from objects getting stuck.

An interesting use of the collision detection option in objects is for dynamic hair. When the collision detection option in an object's properties is turned on, the dynamic hair simulation will try to prevent hair from penetrating that object.
Again, the more collision objects, the slower the hair calculation will be. Using low-resolution proxies greatly speeds up calculation (try kirwyn's free dynamic hair figure, and find out how fast dynamic hair calculation can be).

Tip on using IK: if IK is turned on, you can parent that body part to something else. For example, you could parent a figure's feet to the pedals of a bicycle figure, animate the bicycle pedals and the fgiure will have a pedaling animation.
Other use: let the figure grip a two-handed item (a rifle, a greatsword, a broom), parent both hands to that item, and you can pose the item and the arms and hands will go with them.
Setting "use limits" on the Figure menu is useful here, it prevents the IK calculations from returning impossible values (looks like a wrist or ankel getting badly mangled).

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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