:edit: I read through all the responses
In terms of classes and learning, I know we're talking about ISFJ but someone mentioned similarities in terms of sturctured learning wtih ISXJ.
I think the differences between my ISTJ friend and myself are textbook type differences.
She takes classes to master things and she really hits the books and accomplishes all the goals of the class. Me? Honestly I'm likely to drop the class 1/2 way or lose interest or give up on it (like ceramics...wrestling with the potter's wheel is not fun and I didn't bother picking up my deformed and shameful little ashtray from the kiln)
She's very technical minded, to the point she's been added to the 'help desk' list-serv at work and the IT people include her on e-mails and assume she knows as much as they do. Also, I had a plasma flat screen TV for about a year and never figured out how to get over the air channels on it. She fiddled with it for about 15 minutes and got the channels up! I asked her how she did it and she refused to tell me and told me to read the manual. Personally, I didn't care I was just happy to have the channels up.
She also went to Spain and Italy to learn the respective languages and did a pretty good job immersing herself. She's much more likely to be hanging out with friends, travelling, biking, or even watching tv than on an online forum. I think she would probably find a 'social' (versus technical) forum pointless and unentertaining unless she was having trouble meeting specific groups of people IRL. Though she did start her own e-mail list to keep track of goings on and events amongst a larger circle of people.
I know, it's anecdotal, but FWIW.