To me, an import function of this website is the list of favorite problems. I use it to practice problems that I have difficulty with, and it does help a lot. However, I wish it could have more functions, such as showing various statistics of each problem (average/max/min time used to solve it, correct/total trials, date of last trial, etc.), showing snapshot of the problem when the mouse cursor is over its link so that the player quickly knows what the problem is like, randomizing/sorting the problems based on various statistics (or problem type), etc.
Some of these functions require additional server storage space (average/max/min time, date of last trial). Others may need lots of programming. However, I believe that these functions will greatly enhance this web's role as a place for dedicated users to practice, instead of a place for random users to solve problems on the fly (which is fine, but I guess most web masters prefer dedicated users).