I know a couple online and a couple IRL (hubby is one). They like structure and, therefore, bullet-point lists.
* Excellent system analysts -- This gets them in trouble with the sensitive, at times, but they are great at:
- dissecting any system,
- thinking of ways it would run more efficiently,
- developing a main plan as well as contingency plans on how this efficiency can be achieved, and then,
- either communicating the plans so others can implement them or actually doing it themselves.
* Objectively and sincerely kind -- When they care about another, it is genuine compassion and empathy. It is expressed by taking the time to think through solutions to the problem and making suggestions (or implementing the solution, if the person in need is helpless). What I admire about them is their objective analysis of when to help and when to walk away. They value their own time, wanting to make themselves as productive in the time frame as possible. If the person rejects the help or insists on getting into the same situation repeatedly ("lost cause"), then the INTJs I know will walk away.
* Style of humor is adaptable and they monitor well where to use each style. If they respect you but don't know you well, they'll tune the style to be light and general (non-offensive to most). If you haven't earned respect, they'll either not express humor at all or say just enough to get you to move along. If they respect you and know you well, their natural, unfettered style (sharp, sarcastic analogies; dry; intelligent) is great (George Carlin or Douglas Adams rather than Adam Sandler). It meshes well with my own, so I have fun with them.
* As mentioned by others, very persistent, persevering. Expecially true when they know the idea is worthy and able to make a system better or help others long-term.
* Good at determining the motives and perspectives of others.