One of the reasons some people have cited about going over to Facebook is that Facebook allows you to have a photo on your profile. LinkedIn always seemed to resist, with some people mentioning that it was more "professional" in that you weren't getting into seeing how people looked.
Whatever the past rationale, LinkedIn announced on their blog Thursday that users would be able to upload profile photos. The interface is pretty simple. In your "Accounts and Settings" area under "Profile Settings" there is a link for "My Profile Photo":
Add in a photo and you now have the option to display that photo to your contacts or to display it publicly:
The LinkedIn blog entry goes into more details. Personally, I'm quite glad to see it primarily because over time I find I've lost track of who some of my LinkedIn contacts are and it would be very nice to have a photo to remind myself of exactly who they are. Also, in a global namespace with people having similar names, it's nice to have the visual confirmation when searching that the profile belongs to the person you know. Now it will be interesting to see how quickly people do or do not upload photos.