If you are into marketing, then you already know by now long tail keywords are very important aspect of your marketing plan; Choose the wrong keywords, and you probably already know by now what happens, nothing, and pick the right keywords, then watch traffic come in... and I am pretty sure that no-one attempts to guess LTK or the right keywords to choose, as this would not be wise if you were unsure.... I am sure some will say google keyword tool, but since when did google ever give you all the data you need to make a very good decision? Every now then I may even sure a free keyword tool such as: wordtracker.com But it does me no good to see the keyword at the top and no other data...Just because there is a top keyword listed does not mean you will be able to capitalize on it, so the data that i see from using this free tool is very poor to non-existent. So what software do you use to perform your keyword research?
Here is another free one: ubersuggest.org (You get what you pay for, normally little to nothing in return)
Maybe this is not a good answer to your question but what I do is to do google search with your long keywords. I have free plug-in using SEO Quake in firefox that shows keywords, page rank and other good analysis to sites you are looking at.
I think I am asking the wrong question.... how do you know what long tail you are looking for when you use your software? I can only guess what people are searching for; so how do you know what long tail keywords you are going to search for, in order for the best results?