Version:            (using KDE 4.1.96)
Installed from:    Compiled From Sources

In Konqueror 3.5.x, as with other completion-offering applications like vim and zsh which offer a "cycle through completions by default" mode, Tab can be used to cycle through completions in the address bar.

However, in Konqueror 4, Tab instead switches widget focus to DolphinPart. I consider this a big step backward in usability since Tab is a strong habit, Tab is what everything else uses for completion, and the down arrow key (the only alternative I know) requires that I lift and move my right hand each time I want a completion)