I would like to know what version of grep is being used? GNU or BSD grep? My money is that it is a OSX box with BSD grep.[1]

Using a clone of linus' kernel on a six year old amd64 box running debian/sid:

  (master):dfc@fob-xray:~/lk$ time git grep "leap second" > /dev/null

  real    0m0.739s
  user    0m0.540s
  sys     0m0.650s
  (master):dfc@fob-xray:~/lk$ time grep -r --exclude-dir=.git "leap second" . > /dev/null

  real    0m0.833s
  user    0m0.400s
  sys     0m0.430s
  (master):dfc@fob-xray:~/lk$ du -sh .
  1.4G    .

[1] http://lists.freebsd.org/pipermail/freebsd-current/2010-Augu...

ADDENDUM:

After running a test on a Mac mini with 10.8.4 and a clone of the same repository I am overly confident that the title should be "BSD grep too slow? Use git-grep or GNU grep":

  jumbo:lk dfc$ purge ; time grep -r --exclude-dir=.git "leap second" . > /dev/null

  real	1m8.479s
  user	0m32.229s
  sys	0m2.348s
  jumbo:lk dfc$ purge ; time ggrep -r --exclude-dir=.git "leap second" . > /dev/null

  real	0m41.844s
  user	0m1.682s
  sys	0m6.035s
  jumbo:lk dfc$ purge ; time git grep "leap second" > /dev/null

  real	0m37.325s
  user	0m1.423s
  sys	0m4.213s
  jumbo:lk dfc$ gdu -sh .
  1.3G	.

You can read `ggrep` as either GNU grep or good grep.