Situation: we have two layers in GIS project — 1st contains polygon object to be divided into the cover features; 2nd contains line objects as the borders of the cover features. I can be solved with advanced toolbar of DigitizingPlugin for QGIS. This free but powerful software has just made my day (see picture below, clickable).
In order to divide polygon layer with line of another layer, select feature to be divided, select cutting-edge line feature then choose button «split selected features with selected line» from appropriate toolbar. Pretty simple!