Some numbers on a MacBook Pro 2.53 GHz Core 2 Duo
commit bb5899c56e33716db724cb60a5120b91f5fccdeb
Firefox 3.0.15: 28 ms/instantiation
Safari 4.0.3: 15.02 ms/instantiation

commit 2847c1cf1a2874e9fe56b5749e6e105e37bb086a
Firefox 3.0.15: 49.27 ms/instantiation
Safari 4.0.3: 24.48 ms/instantiation