In the detailed contact view with the opportunities tab showing, the dialogue box for adding that contact to the opportunity is broken in my not so humble opinion. I've been asking for a fix for this to be fixed for more than 2 versions.
When adding a person to an exisiting opportunity, the user has to type very fast otherwise the field is filled in and the user has to back up or start all over again. Even if the backspace key is used, the system will then attempt to autofill completely, not based on what has been typed - or at least the best I can tell.
Please fix this in the next service pack. This certainly distracts from the user experience.