Revisiting the Basics of Java

About twice a year, I like to revisit the basics of the Java API to see if my experience has given me any new insight on how a forgotten (or written off) library might be used on future projects. Right now I'm reconsidering Java Assertions (added to JSE in 1.4), and am curious to hear how you are using this in your own work. Do you use it in lieu of, or in concert with, a testing framework (i.e. JUnit)? I'll be posting my own thoughts on the subject shortly...