This from the (Java 2) javadoc entry for java.util.Vector: The Iterators returned by Vector's iterator and listIterator methods are fail-fast: if the Vector is structurally modified at any time after the Iterator is created, in any way except through the Iterator's own remove or add methods, the Iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the Iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. The Enumerations returned by Vector's elements method are not fail-fast. So... if Enumerations are not "fail-fast" what are they? Fail-slow? Don't-fail? And if they don't fail, does using an Enumeration lock up (synchronize) your Vector until you are done enumerating?
Enumerations do not consider the possibility of concurrent modifications, so if you do not do appropriate synchronisation and/or checks yourself, you may skip or double-up on elements, if there has been a modification since you started enumerating. At least, that's what I conclude from the JDK source for Vector (implements the enumeration) and AbstractList (implements the iterator).
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.