The following currently fails in Eshell:

$ sudo bzgrep # Or any shell script in PATH
/bin/sh: /sudo:root@localhost:/usr/bin/bzgrep: No such file or directory

This is apparently so because eshell/sudo translates that to a Tramp remote
location, but eshell-external-command fails to handle it as a remote
command. It instead passes the default-directory containing Tramp syntax
directly to the command (shell script), which obviously fails as it doesn't
understand Tramp syntax. The patch below fixes this issue. (Was there any
specific reason for earlier only considering "ftp" being remote, instead of
all Tramp methods?)

--- esh-ext.el.orig     2011-02-18 20:57:50.000000000 +0200
+++ esh-ext.el  2011-02-18 20:58:12.000000000 +0200
@@ -203,7 +203,7 @@
 (defun eshell-external-command (command args)
   "Insert output from an external COMMAND, using ARGS."
   (setq args (eshell-stringify-list (eshell-flatten-list args)))
-  (if (string-equal (file-remote-p default-directory 'method) "ftp")
+  (if (file-remote-p default-directory)
       (eshell-remote-command command args))
   (let ((interp (eshell-find-interpreter command)))
     (assert interp)