Comment 5 for bug 203217

Same behavior observed on another system with large NIS passwd file.

$ apt-cache policy fast-user-switch-applet
fast-user-switch-applet:
  Installed: 2.22.0-0ubuntu2
  Candidate: 2.22.0-0ubuntu2
  Version table:
 *** 2.22.0-0ubuntu2 0
        500 http://ubuntu.media.mit.edu hardy/main Packages
        100 /var/lib/dpkg/status

It seems to be doing a lot of gtk work, probably to display users to switch to, e.g.
$ ltrace -o /tmp/trace -p $(pidof fast-user-switch-applet)
^C
$ awk '{print $2}' /tmp/trace | sed 's/(.*$//' | perl -lne '$F{$_}++; END { foreach (keys %F) { print "$_ $F{$_}"; } }' | sort -n -k 2 | tail
_instance_is_a 35
g_cclosure_marshal_VOID__OBJECT 40
g_signal_connect_data 45
<... 63
gtk_menu_attach 31686
gtk_menu_get_type 31686
gtk_menu_reorder_child 31687
g_type_check_instance_cast 123389
g_utf8_collate 182765