You can *browse* your contacts. This is something you can't with the autocompletion simply because the limited number of results displayed. But auto-completion lets you search your contacts, thats why I considered the search feature within the address book widget less important. But that doesn't mean it will never appear there.
I added a search function in my addressbook plugin on specific request from quite a few others out there with company LDAP addressbook consisting of hundreds or even thousands of contacts. Apparently without a search function it becomes useless :)
If I remember correctly, some LDAP systems dont even allow a full listing but only do search, but im not positive.
Cor