This is a difficult topic, because they really are SO similar, as I've discovered. But here after some research I have decided on some probably accurate conclusions.
-INTPs must be exhausted by social interaction
-ENTPs must enjoy spending time with people
-INTPs are ONLY interested in theory and have no desire to impact the real world
-INTPs do not like to bounce ideas off people and have a linear internal thought process
-ENTPs can not finish anything
The dominant Ne in ENTPs means they are LESS (noit to say they aren't) concerned with logical accuracy and are more likey to go with ideas right off the mark than INTPs. This can sometimes mean they rush into situations too quickly but often means they are good at improvising and coming up with a large quantity of ideas in a short time frame. They have a tendency to not follow too deeply into their ideas because they are always coming up with new ones, but if an idea appeals enough, they can potentially carry it rather far, and the ENTP will usually want to put a strong mark on the world with it. When strongly enthusiastic about something, the ENTP can put in a tremendous amount of energy, usually in a very short time frame, into making it a reality. Also, having a higher Fe, they generally have more desire for social admiration and a better ability to enthuse people, becoming motivated by people supporting their ideas and plans. It is not always the case, but they tend to enjoy generating ideas with people. They tend to view most of their life as a new experience as opposed to relating it to things they have done before, and will normally try new and experimental approaches, preffering to see where it takes them rather than being cautious. They tend to be quick witted and prefer thinking quickly n the spot. They are less likely to get caught up in logical details and are more big picture people, which often gives them stronger leadership ability and greater skill at carrying ideas forward into reality quickly. Because of this, they tend to also be less limited by logical principles, giving some ENTPs the competitive but less sincere aspect that INTPs tend to lack.
The primary Ti means that in general, the INTP will be more focused on smaller details and logical principles. They still generate ideas, but they tend to be less diverse and numerous than the ENTP. An INTP however, tends to think through ideas in more depth and while generally not as good at carrying ideas out are better critics and analysts, noticing minute logical inconsistencies, which can seem very important. While the ENTP is an idea generator, the INTP is an idea perfectionist. They will also be more likely to examine whether something they are doing fits within their principles, or if it has proven to be useful and safe in the past with Si. INTPs do not necessarily have a thought process seperated from the world completely. Their Ne is present in the external world still and will often look for input in others, but the difference is that the INTP theorises internally and uses Ne to get input to expand on the concept, whereas the ENTP uses Ne to get ideas and then Ti to verify them. In fact, because Ti always searches for truth, the INTP may constantly search for more input if they doubt their conclusions are accurate (this was one thing that had me thinking I may be ENTP at one point, as I frequently search for input from others). They are generally quite cautious and must be sure of something before they act on it. The INTPs thoughts may also be rather tangential, but they will be more likely brought back to a single or few conclusions. They will always be striving primarily for accuracy, and a lot of the time, simplyunderstanding an idea in depth will be enough. However, that is not to say an INTP will not want to interact with the world. They still have Ne, and will often enjoy sharing their logic systems and ideas with the world, and even implementing them in a useful way, once they have been thought through thoroughly. Because INTPs have low Fe, they tend to have less desire for people to support their ideas, but are also generally less gregarious and have little skill for getting people on their side. The INTP often has a strong aspect of sentimentality towards things that relate to them personally or are part of their past.
Hm... well I hope I covered most of the important stuff and didn't make any mistakes. I think there are a lot of misconceptions, but perhaps I have my own misconceptions here. What do you think of this? Is it a good way to differentiate the two types?