I think this feature can still be improved:

-There should be an option for resetting all the exercises you have done (you can do that in Chess Mentor)

-One should also be able to create his/her own list of problems (I mean, like a youtube playlist)

-The computer still  doesn't allow castling.

    Although there are more options that need to be added, I think "Computer Workout" is the best feature of the whole site.  It allows the intermediate player to review the more difficult chess positions.  Its like having a chess coach who gives no hints.  Although the "hint" button is present some the of problems have no hints like the "Extra Bishop: Benoni" problem. Some one forgot to fill in the dialog box.

After 5 hours on the "Extra Bishop: Benoni" problem, I found an attacking line thats scored as high as +5.20 points but the computer quickly drops that to +2.30.  Look at my attacking line and judge whether its a valid attack or is it busted?

1. a3 Rc8 2. b3Nf5 3. Ne4Nd6 4. Nc5Bg4 5. h3Bh5 6. g4b6 7. gxh5bxc5 

 8. bxc5Nb7 9. Nh4Nxc5 10.Bd5+ Kh8 11.Ng6+hxg6 12.Ne6Qh5+

Note: white's option to 12. Bf7 also looks promising but Black quickly defends.