Learnability
On any of the add/edit pages, this design is quite learnable. It uses a form interface in a way that should be familiar to most internet users. All fields and buttons are clearly labeled with the information they contain or the function they perform. The only exception to this is the task lists, which add or remove items with a button containing + or -. The meanings of these symbols are relatively obvious in context, however. Furthermore, the use of + or - symbols to mean "add" or "remove" is consistent within our task editing pages, and is not uncommon in websites in general.
The main page is also highly learnable. Although the documents and companies boxes are not labelled, the add buttons under each effectively say what goes in the box. One possible difficulty is that these boxes might look like text areas to a new user, who might think that the "Add document/company" button works like a submit button. To improve learnability (as well as to prevent errors) we can remove affordances for typing in these boxes, perhaps by coloring the boxes and certainly by not allowing the user to visibly give them focus or see a blinking cursor.
Visibility
This design shows a lot of information on its main page - all of the documents, all of the companies, the categories of the companies, and the most pressing task for each company. Every task currently accomplished is visible a click away from the main page. Additionally, when the user adds a document, company, or task, any changes this makes to any display is visible upon submission of the form. The state of the information the user has added to JobTracker is therefore quite visible.
One thing that is invisible is history. The user can see what documents, companies, or tasks are currently in the system, but as soon as they are deleted, the user has nothing but her memory to tell her they were there. This is not particularly important, however, because the user is unlikely to care about her history of changes.
Affordances are appropriate to the function of the components (with the possible exception of the boxes, as described in Learnability). The design is not cluttered, but contains enough text that the user can easily understand what each component is supposed to do.
Perhaps the most problematic visibility aspect of this design is the location of the add buttons on the main page. The bottom of the page is not necessarily the first thing that will capture the user's attention. The design is so simple, however, that this is unlikely to represent any substantial difficulty.