This drastically speeds up require time on ruby 1.9 (17s down to 10s in our production rails app) , at the expense of disabling some edge case handling around autoloading. YMMV but it works for our rails app.

ruby_require_speed.patch

From 2fb8432982b7e8ffc4c05f912f47cd9ca7261427 Mon Sep 17 00:00:00 2001
From: Xavier Shay <[email protected]>
Date: Sun, 1 May 2011 10:25:18 +1000
Subject: [PATCH] Disable some edge cases in requiring to speed it up.

---
 load.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/load.c b/load.c
index f8f0551..a14cc93 100644
--- a/load.c
+++ b/load.c
@@ -152,6 +152,7 @@ rb_feature_p(const char *feature, const char *ext, int rb, int expanded, const c
 	f = StringValuePtr(v);
 	if ((n = RSTRING_LEN(v)) < len) continue;
 	if (strncmp(f, feature, len) != 0) {
+      continue; // Pretty sure we don't need the behaviour below this line
 	    if (expanded) continue;
 	    if (!load_path) load_path = rb_get_expanded_load_path();
 	    if (!(p = loaded_feature_path(f, n, feature, len, type, load_path)))
-- 
1.7.3.1

I get similar sorts of performance gains too. Awesome!