Interesting thread. I'm not ISTJ but my sister and father are and some of the similarities are funny to observe. And now to give you some traits we may share, given we only differ one letter. I'll make some notes about my relatives too.
Learn best by seeing and doing - I can sometimes copy, but normally I like to go my own way after getting the general idea.
Excellent analytical thinker - I overdo this, I think.
Dry/Sarcastic humor - Sometimes, sometimes not, usually I'm not interested in humor if it'll only avoid a good conversation about something that will be useful to learn, but my humor is different from yours.
Great awareness - I can if I want to, like I see kids acting up when nobody else does but otherwise I'm a daydreamer.
Can only focus on one thing at a time - No, I normally need something to spin in my hands while talking. (I don't know)
Extremely private - Used to be, wish I still was. It's useful. (Whole family is.)
Poker face always present - Yeah. (This is only me)
Socially retarded - Yep, especially when emotions are involved. (My sister is. XD)
Very observant - Depends on what we're observing, but usually I tend to miss obvious things, but point out things others don't see. (I don't pay attention enough)
Easily annoyed - I don't think this is related to type, but I'm not easily annoyed. (My dad is.)
Take everything literally - I feign this in sexual discussions, but I'm good at picking that stuff up. (My family members are decent at this too, but they're not high on the "S" and are pretty intelligent.)
Often have errors when forced to make quick decisions - Not enough data.
Procrastinates - This is my special talent. (Present in both ISTJ family members)
Selfish - I'm not completely selfless, but I'm not selfish. I don't think type has to do with this. (Not present in either ISTJ family member)
No style - Yep. My color is black.
Hate cleaning - This is just laziness for me. (Which runs in the family, but sucked because my dad always wanted the house cleaned EVERY day.)
Health conscientious - I am somewhat. My two family members are too, but I'm better off in that department than they are, if you know what I mean.