I installed the Safari 4.0.4 update yesterday on my OS X 10.5.8 (Leopard) and got GWT 1.7.x crashes ever since then. That’s a pitty since I’m involved in a larger GWT project (featuring GWT Canvas). There’s already a ticket and a simple workaround available but that’s no choice for production environments.
So if you have a Google account, please vote for it so it gets resolved soon. Apparently it’s a Webkit bug which will be fixed in Safari 4.0.5.
Update: I could downgrade back to Safari 4.0.3 using Pacifist and the Safari 4.0.3 installation package. I opened the package with Pacifist and chose “Replace” as the option for all files. Trying to apply the package alone won’t help because it detects that a later version was installed, even if you try to remove Safari competely using AppZapper.
Safari’s “About” screen shows version 4.0.3 again, OS X asks me to update to 4.0.4 again and my GWT application is back running. Not sure whether there are any other side effects, though, so handle with care.
Another update: Someone wasn’t as lucky as me and screwed his system with that approach. Better follow this instruction.