UML: Sequence, Activity or State?

Do you find yourself torn between modeling types for your component? These rule-of-thumb's from Martin Fowler's book "UML Distilled" may come in handy!!

"You should use sequence diagrams when you want to look at the behavior of several objects within a single use case. Sequence diagrams are good at showing collaborations among the objects; they are not so good at precise definition of the behavior."

"If you want to look at the behavior of a single object across many use cases, use a state diagram."

"If you want to look at behavior across many use cases or many threads, consider an activity diagram"

http://stackoverflow.com/questions/150445/can-a-sequence-diagram-realistically-capture-your-logic-in-the-same-depth-as-code

Simple Semantic Context Brought to You By Typedef

You vote: Confusing as heck or extremely useful?

The typedef specifier in C++ allows you to add that little bit of context that may be missing from your variable's type.

The following statement tells us that our property is not just a collection of Strings, but a collection of Strings that represent first names. 

typedef vector<bstr> FirstNames;

FirstNames mtvFirstNames;

The variable name implies the additional type context to me, but hey... I'm a Java developer.

Is there some uber niche where this comes in really handy?