From the Gnome 2.10 release notes:
In the past, while typing something into one application when suddenly your instant messenger offered a chat request from your friend, your words would be typed into the chat window. Imagine if you were typing your password at the time. This should no longer happen in GNOME 2.10.
In addition, if an application takes a long time to start, your work will not be interrupted when it finally opens its window.
About time someone fixed this! The window focus-stealing problem has plagued just about every desktop out there. I think Windows is the first one I noticed that attempted a solution (blinking the taskbar button instead of switching to the dialog box). And since I often fire up several programs at once, it can get really annoying when I start typing my password into one, hoping I’ll finish before the other window appears and drops the last three letters into my web browser or something.
Unfortunately I’ll probably have to wait for Fedora Core 4 to really use it, unless I want to go even more bleeding-edge than I already am.