w stopped working?

[Eamonn Sullivan]

I use the w command often when working on Ubuntu because I primarily
use it from a wirelessly connected laptop via VNC. I use w to check if
any of my kids are logged in on the computer (which is on the other
side of the house), if i need to restart or do anything cpu intensive.
Normally, when I run the command, i'd see myself and who ever is
logged on upstairs (or via another vncserver connection) like user:0
or user:1. However, in the last week or so w stopped working. Now I
just get:

esullivan at gandalf:~ $ w
 15:03:32 up 1 day, 16:14,  2 users,  load average: 1.20, 0.89, 0.93
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
esullivan at gandalf:~ $


Almost certainly this is my fault (i.e., pilot error), but what
configuration files control this? Where should I check?

-Eamonn