Before Zimbra can effectively compete with full-on contact mangers like Act or GoldMine it will need to facilitate storage and searching of custom field data.
For example, I don't need any of the "Other" area fields in the contact manager, but I do have need for fields named "Source", "Acquired", "AssignedTo", "LastAction" and "LastDate", etc. I am having some success using otherwise unused fields for these purposes, It would be very helpful if I could give them meaningful names.
There is an RFE in Bugzilla at http://bugzilla.zimbra.com/show_bug.cgi?id=10056
If this feature seems valuable to you please go to Bugzilla and vote for it.