I happen to be working on a lengthy functional description of IEE at the moment...
What I have noticed is that, as with other types, initial behavior can vary widely from IEE to IEE depending on how much the person identifies with the situation and the people there, whether he is a socialite or a "selective communicator," etc. I'm definitely the second type, and in some situations I can be very reserved, but yet at the same time always extremely observant of everything going on. In large groups with an

feel, I usually keep to the sidelines until I gradually get to know individuals. I can identify with Mikemex -- not really participating, but not feeling unconfident because of it. It's funny to see SLIs sometimes jump into groups, quickly get disillusioned and/or burned, and then reject much of the group,
while IEEs sometimes do just the opposite -- holding back, selectively building relationships, and eventually becoming prominent in the group. If the group's not for me, I usually never show my "true face," and people never have an accurate impression of me.
In more formal situations like meeting a new potential partner, giving or taking interviews, making initial contact with people, etc. most IEEs feel confident and seem very extraverted (me included). I've known one IEE, however, who hadn't developed a "I'm a really competent guy" persona and instead holed up and didn't say much in these situations, which seemed strange to me.
I know a couple IEEs who said they didn't become their normal outgoing selves until they were in their 30s. I see this in myself, too (I'm 29). Each year brings more social confidence and less fear. Some younger IEEs try to live like hermits or "closet intellectuals" who sit home and do some "great" work, but age seems to always pull them out into the real world, where they end up staying. In any case, I don't know a single IEE who can stay balanced after spending the day alone. Often, they (we) are clueless about what our basic needs are and try to ignore them -- including social needs. Often IEEs think an "abstract connection" with people they've never met or barely know will do, but it doesn't. There has to be eating together, walking and talking, etc. etc.
ramble ramble... ...