Pretty self-explanatory. You can't do anything in GNOME while SlashApp is loading headlines. If this takes a while, or forever because there's something wrong with either your network connection or the slashdot site, the panel is completely useless. This is bad. It means the pager is unusable. *Anything* under the panel is unusable. And if you start messing around by clicking around the panel, or killing the slash_applet process, you can hose your GNOME panel config pretty badly.
I have confirmed this to be true on a standard 6.0 install in our test lab. If the ethernet device (or ppp) is taken down while the slash applet is running, the panel no longer accepts input. When the network is again usable the panel eventually comes back. This has been assigned to a developer for further review.
There is a workaround for this problem in the development version of gnome-core.