I came from MBTI, and while I have adapted to the differences of socionics and MBTI, I still have to think for a few seconds just to figure out who's who.
Here are the un-ergonomic problems I've observed:
1. 'E's are used to represent both extroverts and feelers.
2. 'I's are used to represent both introverts and intuitors
3. When converting 3-letter to 4-letter, the first letter I'm going to figure out is E/I, but the E/I scale is at the end of the 3-letter system.
This is the 3-letter system that I would feel most comfortable with:
ENTp = ENT
INFj = IFN
ISFp = ISF
ESTj = ETS
and so on.
(On a side note, I'd like to say that socionics is so much better than MBTI. In socionics, I can understand and empathize with every IM element and every sociotype. In MBTI, most types just don't make any sense to me, upon first observation. Everything is beautifully and mathematically laid out and socionics has so many more interesting dichotomies. I just wish it was more popular in the Americas and on the internet.)