tk-8.5.2-alt1
gitk-1.5.5.5-alt1
openssh-5.0p1-alt3
openssh-server-5.0p1-alt3
xorg-server-1.4.2-alt10.M41.1
(in Desktop 4.1)

How to reproduce:

[imz@localhost ~]$ ssh -X 0
imz@0's password: 
Last login: Tue Apr  7 18:42:59 2009
[imz@localhost ~]$ mkdir tmp/test-gitk
[imz@localhost ~]$ cd tmp/test-gitk
[imz@localhost test-gitk]$ git init
Initialized empty Git repository in .git/
[imz@localhost test-gitk]$ echo a > a.txt
[imz@localhost test-gitk]$ git add a.txt
[imz@localhost test-gitk]$ git commit -m "Initial."
Created initial commit 681640e: Initial.
 1 files changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 a.txt
[imz@localhost test-gitk]$ gitk
X Error of failed request:  BadWindow (invalid Window parameter)
  Major opcode of failed request:  38 (X_QueryPointer)
  Resource id in failed request:  0x74
  Serial number of failed request:  2798
  Current serial number in output stream:  2798
[imz@localhost test-gitk]$ 

When it crashed, I tried to select the "Tree" view on the right. (It also crashes in "simpler" cases: run in any directory, even without a "git init".)