Hi all,
I just created new wiki page about performance issues GRASS vs.
ArcGIS, see [1]. Any other examples are highly welcomed 
Martin
[1] http://grasswiki.osgeo.org/wiki/Performance_issues_GRASS_vs._ArcGIS
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Martin Landa <landa.martin gmail.com> * http://geo.fsv.cvut.cz/~landa