Here is a patch for the troubleshooting.textile page. Hope this is good!
--- troubleshooting.textile (revision 680684)
+++ troubleshooting.textile (working copy)
@@ -119,3 +119,20 @@
+h2. buildr fails to run after install with a "stack level too deep
+A particular quirk of an existing ruby setup can cause problems when running
+buildr. If a system already has several ruby directories that are in the
+PATH, it is often nice (appropriate?) to have them in RUBYLIB as well (to be
+able to require them). If there are several of them a user may decide that
+RUBYLIB=$PATH is a good way to handle this (or some less automated method
+that has the same effect).
+If you see an error running buildr that shows the "stack level too deep"
+error, it is probably your RUBYLIB environment variable. Removing the bin
+directories that have buildr in them is probably the solution. Removing all
+directories that you don't actually need is probably the appropriate measure.