Tiger update 10.4.11 installs Safari 3, which seems all well and good. But it left Safari almost completely unusable. I could trick it into showing me a page by Cmd-clicking to open the URL in a new tab, but neither just typing in the URL and hitting return, nor clicking a link from bookmarks would launch it.
I noticed on Zeldman that he was having the same issue (albeit more seriously, leading to instant crash) to which a commentor suggested removing InputManagers. I removed just PicLens which cleared up the problem. Needless to say, the latest version of PicLens doesn’t have this problem.