It's in the context menu for tasks, right? We brought that feature over from Outliner but haven't had time to make it work yet, so we've turned it off until we can do it right. We meant to hide it completely, but I guess we missed one spot. Hopefully we'll add this feature back soon.
Also, you can import from address book -- it's in the context menu for the resource view. Email
omniplan@omnigroup.com if you need more help finding it.