I created a highly-efficient tool, called lasboundary (1,2), that computes a concave hull for LIDAR in LAS/LAZ/SHP/ASCII format and stores the result as a vector boundary polygon in ESRI Shapefile format or a geo-referenced KML file.
Here is an example run:
C:\lastools\bin>lasboundary -i SerpentMound.las -o SerpentMound_boundary.shp
reading 3265110 points and computing convex hull for 3265110 points
growing inward towards concave hull (with concavity = 50)
outputting the concave hull
concave hull has 1639 points
Some result pictures are here.
