I think it would be worth the effort and well received to develop these capabilities. We use Highrise now, and the whole bcc:/forward approach to linking in emails is a pita. It is especially frustrating that if you forward an old email, it is linked as of the day you forwarded it, and if you forward an email you just sent but forgot to bcc: your dropbox, the email is linked to you, not the original contact(s).
Being able to link in emails (as of email timestamp) directly from Gmail would be a real win for Zurmo.
Calender CRUD integration would be fantastic.
Also would like to see better Google Map integration, e.g., pins of all contacts in the displayed region, and be able to filter by type, keyword/tag, etc.