qgis/Quantum-GIS — pull request #338 by simon04 (2012-11-25 11:17:56+00:00)
Title: Abort classification upon high number of classes

Accidentally classifying a vector layer (categorized style) on an id column (with >99k unique entries) resulted in high CPU load and QGIS frozen.
I suggest to present a warning dialog when more than 1000 unique values are present and ask the user whether to continue. Patch attached – please check for usage of correct terminology.