It certainly wouldn't hurt to be familiar with them. Most important points to know about them probably would be that they are immutable and final.
You should also know what kind of constructors each has and the constants defined for them such as Double.NaN, Integer.MIN_VALUE, etc.
Off the top of your head, can you answer the following question?
Question: Is the following code legal?
double d = Double.MAX_VALUE;
Float f = new Float(d);
[ January 30, 2002: Message edited by: Junilu Lacar ]