...that you can select whether the week starts on Monday or on Sunday in the System Settings? KOrganizer uses this setting. Look at Locale->Country/Region & Languages in the System Settings, or select Settings, Configure Date & Time... from the menu bar. Select the Calendar tab.

...that you can edit to-dos quickly by right clicking on the property you wish to change; like the priority, the category or the date?

...that your calendar can display birthdays from your address book? It is even possible to set up reminders for them. To activate this, add the corresponding 'birthdays' calendar from the Calendar Manager.

...that you can store your calendar on an FTP server? Use the standard file dialog to save the calendar to a URL like ftp://username@ftpserver/filename. You can make your calendar active and load and save it as if it were local, or add it permanently to your calendar list, by adding a remote file from the Calendar Manager. Just make sure that no two KOrganizer applications are working on the same file, at the same time.

...that you can create hierarchical to-dos by clicking with the right mouse button on an existing to-do and selecting New Sub-to-do from the context menu?

...that a color can be assigned to each category? Events with a certain category will be shown in that color. You can assign these in the section Colors within the dialog which appears after selecting Settings, Configure KOrganizer... from the menu bar.

...that you can view and edit a calendar with Konqueror? Just click on the calendar file to make Konqueror open it.

...that it is possible to add an attachment to an event or to-do? To do so, add a link to the Attachments tab within the Edit Event or Edit To-do dialog.

...that you can export your calendar to HTML? Select File, Export, Export Web Page... from the menu bar to open the Export calendar as web page dialog.

...that you can purge completed to-dos in one step? Go to the File menu and choose Purge Completed To-dos.

...that you can create a new sub-to-do by pasting a to-do while another one is selected?