We purchased the network version almost 6 months ago. I put off the upgrade due to v5 coming out. I was very nervous about upgrading after seeing people talk about having to dump ldap/mysql and reimporting. I didn't have to do any of that, here is how I upgraded ours. Ours started having problems around 2pm yesterday, a hard drive in the raid was failing and some DNS issues(I think). We had a new asus 1u RS162-E4 w/ 4 gb corsair, dual quad core 5335's, 4 500gb seagate server satas. I plugged in a ext usb hd and did the following on old server.

fdisk -l to list the usb hard drive
fdisk /dev/sdc1

delete any old partitions, and created a new one (primary), w to write and save out.

mkfs.ext3 /dev/sdc1 (formats partition on usb hd ext3)
mkdir /migration
mount /dev/sdc1 /migration
su zimbra
zmcontrol stop
exit (back to root user)
rsync -avr /opt/zimbra /migration

3 hours for 81gb of data on 241 accounts

while it was doing that, We installed centos 4.6, took basic server install, disabled firewall/selinux. We set up the onboard raid using enhanced mirror which is raid 1,0 i think. Centos sees all 4 drives as one partition, took defaults on partitioning. rebooted, did yum update, etc. Unplugged usb hd and plugged it into new server.

fidsk -l to see where to mount
mkdir migration
mount /dev/sdb1 /migration
screen rsync -avr /migration/zimbra /opt (i screened it off to do other stuff)
fix ip, hosts, turn off sendmail

get ready to install zimbra
yum install compat-libstdc++-296
mv /opt/zimbra /opt/zimbra_ori
installed using -s option (no config)
rm -rf /opt/zimbra
mv /opt/zimbra_ori /opt/zimbra
install zcs-4.5.2_GA_699
made sure everything is back to normal and working

upgrade to zcs-4.5.11_GA_1751.RHEL4
./install.sh --platform-override (since we are using centos)

yum install libtool-libs
upgrade to zcs-5.0.4_GA_2101.RHEL4.20080321155827
./install.sh --platform-override

upgrade to zcs-NETWORK-5.0.4_GA_2101.RHEL4
./install.sh --platform-override (come on zimbra, centos aint that bad!! -lol)
use web admin to install lic file in proper place.

the next day out of 241 accounts, had 3-4 calls mostly about new features.

I used this as my main guide

Thanks Zimbra!

only 1 minor issue, for some reason zimbra will not auto start at bootup, have to su zimbra and zmcontrol start...any ideas?