Joe S. Tudent's thinking:
Why should I, a graduate student and a gentleman, be doing these optional problems? Pointless, no?
EVALUATION METHOD: Weekly homework assignments and a term project individually tailored to student's level and research interests. Grades will be determined from the homework (60%) and the term project (40%).
By doing optional problem sets you can build up capital (ie, problem set scores over 100% right) which will help you through the rough times, problems you cannot or do not have time to solve. A wise investment.