A stock log would make it much easier for users to keep track of what stocks they've bought and what prices they were bought at.
Say for instance today I buy 25000 shares of FRE at 32 TU each, and 25000 shares of FAS at 120 TU each. The log could read along the top
***
Ticket Name/Stock - Shares - Date Bought - Price per Share - Total Cost
FRE - 25000 - 5/17/09 - 32 TU - 800,000 TU
FAS - 25000 - 5/17/09 - 120 TU - 3,000,000 TU
***
Then when you sell all of the shares of a particular stock, that row on the log will disappear, since you don't really have to keep track of stuff you don't have anymore.
I currently keep track of all my stocks on a text document offsite, although I even record the stocks I sell, how much I sell them at and the total and such.