Two years ago I took the professional test courtesy of my college.
The results I received were a dominant and very distinct E and an auxiliary, also very distinct, T. S/N was very close though P was also very distinct.
In the end I was ENTP and I felt that this was an accurate assessment given my understanding of the types.
While not always accurate the test did make a lot of group work significantly easier since everyone knew their type. We used it to easily explain our preferences in regards to brainstorming, group dynamics, and information gathering in ways that everyone understood.
I think, at least for the purposes of what I've used the types for, the E-I spectrum wound up being the most important because it most directly related to how someone tends to gain their energy and deal with their social interactions. The knowledge made sure that I didn't run roughshod over my friends while they were busy formulating thoughts and still processing information. At the same time it also let them understand that when I'm randomly spewing out ideas not all of them are serious, but I made decisions most easily by bouncing them off of other people no matter how inane they are.