LinkedIn has a new Outlook Toolbar 2.0 (came out in March apparently - don't know how I missed it) which has:
- Ability to view mini-profile ('info box') if the email comes from a fellow LinkedIn user
- Invite Contacts from Outlook
- Build Contacts Wizard
- Grab Contacts
Interestingly enough, the LinkedIn and Plaxo toolbars are slightly incompatible and they are apparently 'working together' on the issue.