In the current k3b-0.10.2 ebuild users are called up to run 'k3b setup'. This program doesn't exist in the current k3b release because the k3b setup tool is included in the kde kontrolcenter. The note at the end of the ebuild should be adapted to this fact.
Same problem for me, now i know there's in KDE Control Center... I'm using Gnome (but i have boths). Thanks for this appoint. I think should be a note, too.
fix in portage, thanks for the report.