[Hampshire] Results of du -hs :-(

[lisi@Tux:~]$ du -hs /home

39G     /home
[lisi@Tux:~]$ du -hs /home/lisi
39G     /home/lisi
[snip]
[lisi@Tux:~]$ su
Password:
[root@Tux:/home/lisi]# du -hs /
[snip]
79G     /
[root@Tux:/home/lisi]#

I have an 80Gb HDD. Konqueror reports 5.9 KB for /home, but 15.8 GB for the
largest folder in it. Is it
a) worry time
or
b) panic time

And what realistically could I do about it?

TIA
Lisi