I've just started using KDE-pim, and I'm coming from years of use of a Palm Pilot (with Datebook3), so that's coloring some of my perceptions of the PIM.
Here are some suggestions, based on KDE-Pim 2.0.6 (on an SL-5000D, OE 2.5.3, Opie 1.7):
First of all, thanks for your work in on-going development on these tools. They are my main use for the Zaurus, and it's good to have this software.
kapi
Add the abiility to right-click on the "Category" tab in kapi to quickly filter on existing
categories. (Similar to the "auto filter" option in Excel (yuck), where the existing categories are automatically available for filtering.
On my desktop (Kapi 2.0.23), I can search within all fields of an entry (including notes). On the Zaurus (version 2.0.6), searches seem to be restricted to just name, family name, category, e-mail address.
kopi
Add the option to hide "to-dos" that don't have a due date in the "What's Next" view
Possibly option for floating to-dos (ie., they've got an assigned day, but "float" to successive days if they're not completed)
Add the option to right-click on the "Category" tab to quickly filter on existing
categories.
Add the ability to right-click on the Priority tab to filter (not sort) by priority
Allow assignment of categories to applications (ie., to-do, addressbook,
calendar). Enable the option to determine which categories are visible
in which application (default to the "native" category). For example, I tend to use the "ToDo" list for general reminders that don't have a specific date--such as the names of books that I want to purchase someday, but not today, or my wife's clothing size, in case I'm ever shopping for her. These are not associated with a specific task, but could be grouped into categories like "Books to Get" or "Sizes". Those categories would only apply to the ToDo views (and application), and never need to be shown while entering an appointment or filtering in the calendar view. Similarly, a calender-specific category, like "weekly department meeting" wouldn't need to be visible in when entering (or filtering) the ToDo list.