I saw the post on subtypes and thought I'd put in my two cents, but it probably deserves a new thread.
I personally don't "use" (i.e. don't think about) any of the existing subtype systems. Rather, what I generally apply as I get to know someone is this -- in addition to their socionic type:
1. Are they an endomorph, mesomorph, or ectomorph?
The personality and behavior differences between these three body types are significant enough to warrant making a mental note of it. An ectomorphic LII is different from an endomorphic one, simply by virtue of body type. The ectomorph will be more reserved and will internalize his emotional reactions more, whereas the endomorph will be more emotionally open. Call them " and subtypes," if you will, but I think the somatotypes are closer to the truth.
2. Are they a physical, emotional, or mental person?
Somewhat related to the above, but not entirely. Quite related to socionic type, but not entirely. For example, there are mental IEEs and then there are emotional ones. The emotional ones exert their energy more on people and getting to know them. The mental ones are more distant and focused on intellectual pursuits. Some SLEs are more physical than others. A thin SLE may seem more mental, maybe even ectomorphic, whereas a heavy-set one may seem more physically dominating.
3. How intelligent are they?
I look at the scale and universality of a person's interests, and what kinds of things they are drawn to and excited by. This affects intertype relations, because your "most real" conflictor, for instance, will be someone who's at a very different level than you. Your "most real" dual will be very close to your own level. Have you ever felt sucky in your own quadra because of intellectual differences? Then you know what I'm talking about.
None of these "scales" is discrete, as opposed to socionic types. I prefer to keep what is meant to be discrete, discrete, and what is part of a continuum, continuous.
Another thing that may be very important as well is the degree of social domination.
4. How much do they force themselves upon others?
Two people of the same type may be very different if one of them always demands to be in the center of attention, while the other lets other people have attention and is calm about his place in the group or community. You might equate this scale to the psychological definitions of extraversion and introversion.