I entered successfully into 2nd month of using Zimbra Network edition 4.0.1 . As an admin I have a question regarding Zimbra performance. Many of my new users are complaining on Zimbra's performance especially while using the webbrowser.
Following is the ouput for df -h

[zimbra@testl ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
74G 41G 29G 59% /
/dev/hda1 99M 12M 82M 13% /boot
none 506M 0 506M 0% /dev/shm
/dev/shm 150M 0 150M 0% /opt/zimbra/amavisd-new-2.3.3/tmp
/dev/shm 150M 188K 150M 1% /opt/zimbra/amavisd-new-2.4.1/tmp

The Zimbra server's RAM is 1GB. As you can see that 59% of the space got used, I am afraid to add users any more. I would like to get a suggestion on increasing Zimbra performance, hardware performance and the disk size. Are there any specials steps or rules to follow in doing so?