I just installed Ubuntu 10.10 (actually Lubuntu 10.10, but this should apply) and the Linux Groupwise client (yes, someone uses it) was suddenly not able to open external web links. Some Ubuntu apps use the program "gnome-open" to launch external apps, like web browsers.
In Ubuntu 10.10 the "gnome-open" command has been deprecated and replaced with "gvfs-open". Creating a symbolic link for "gnome-open" which links to "gvfs-open" solves the problem. Like this from a command line :
$sudo ln -s /usr/bin/gvfs-open /usr/bin/gnome-open