well, im an INTJ (on every single online test ive taken as well as the actual instrument itself) and I can be very absent minded about things I don't deem of particular importance. As for impracticality, well, my chosen field of study is abstact maths (granted the EXTREMELY abstract maths like model theory and propositional logic are a bit tough for me, but thats because they ARE tough in general).
You have to keep in mind that the descriptions you read of types are sort of "best fit" kind of descriptions. No one is going to match the descriptions exactly. One description I read said INTJ's very often had very short hair, were thin and walked with their stomach out. Well, my hair is past my shoulders. I'm barrel-chested, and while Im a healthy weight now, in my early teens I was pretty pudgy, and I definately slouch.
Also bare in mind that often that a lot of the type descriptions read like vague astrology "assesements"
http://www.skepdic.com/forer.html
In short, dont worry too much about a test telling you who you are, decide for yourself.