I've got 2 hosts I'm monitoring the SMTP port- when the ports respond zabbix displays a 1.
On 1.6 I created a stacked graph and added the 2 hosts with filled region so I could easy see when one went down.
On 1.8 I can't get the stacked graphs to work properly. I only see 1 of them - it looks like the other is hidden underneath.
I"ve uploaded a screenshot to http://img704.imageshack.us/img704/19/zabbix.jpg