In Zabbix 1.6, I have configured value maps for "Character" items. They are still working in Zabbix 1.8.
However, it is not possible anymore to create a character item with a value map since this field is removed from GUI entry form.
I was able to associate a value map to a character by modifying it directly in database:
mysql> update items set valuemapid=13 where description = 'my item description';
After that, value maps are correctly displayed in Latest Data page.
PS: This bug is similar to
ZBXNEXT-339. I have opened a new bug since it is currently a regression from 1.6 behavior.