Clicking with the middle button on the TV screen mutes sound.
Using the mouse wheel over the TV screen changes channels (direction is configurable).
Right clicking on a channel in the sidebar yields a context menu.
Doubleclicking on a channel in the sidebar opens the URL of the channel.
Doubleclicking on the TV screen changes the view mode (configurable).
You can eliminate noise on channel change using the "Volume restoration delay" in the "Sound" configuration page.
Many useful actions are bound to keyboard shortcuts; look at the "Configure Shortcuts" dialog.
kdetv supports remote controls through KDELIRC (shipped with KDE 3.2 and above).