Because Supermemo (As well as other Spaced Repetition programs) requires that you review a piece of information a minimal number of times, the number of items you must review on a daily basis goes down quite quickly.
For the past couple of years, I have probably reviewed only 200-350 items per day. Thanks to being able to use a Nintendo Wii Remote with my computer, I can now review items almost as quickly as I can recall them; very little time is spent actually pressing buttons (Mainly the A and B buttons on the Wii Remote).
After a bit of reluctance, I have started increasing the number of items I add on a daily basis. As a result, the average number of items has jumped to around 500-650 per day. But strangely, the amount of time I spend on them is around 1 to 1.5 hours; this increased workload has not changed my morning routine much at all (Wake up, do Supermemo, jog, eat breakfast, leave). In fact, rather than feeling more stressed ("Oh no! I have 600 items today!"), I feel more refreshed and excited in general.
(Update on remembering Chinese words: It is indeed working, and I am able to remember words very quickly, although not as quickly as I did Japanese words; before they are "locked" in my memory, I usually get the tones wrong a couple of times.)