Watched the video about sculpting over at blender3d.org . In this video the guy is in sculpt mode and then drags a sort of border and only the vertices/faces in this rectangle are visible and all others hidden. This sounds like a nifty thing to do but how did he do it? How can I rect-select vertices in sculpt mode so all vertices outside the rect are hidden?
H to Hide vertices, alt-H to unhide
In Sculpt mode use Alt-B and then drag and LMB to select the region you want visible. Press Alt-B again to see all.
Does work 
. Nice thing… although speed doesn’t build up as I expected. Still though it works. Fiddled already around a bit with sculpting. Tricky thing 
Don’t use Alt+B in sculpt mode, use Ctrl+Shift+LMB to hide everything outside of a region, or Ctrl+Shift+RMB to hide things inside of a region. This will give you a speed up as expected.
Wow, that is really awesome! Wish I’d known if it sooner.