I basically like it, but stopped using it entirely when I picked up a copy of Zerwick's Grammatical Analysis of the New Testament, which I reference on the list of 'cheats'. I lent Linguistic Keys to my pastor about a year ago and have completely forgotten to ask for it back. Zerwick is much more comprehensive, and is keyed to his intermediate grammar.
However, I am extremely interested in the *two* new editions of Linguistic Keys that are being published in the near future, one by Zondervan, one by Hendrickson. Each of these is much more comprehensive than the original. There was a German update to Linguistic Keys which has not yet been published, and Hendrickson will be publishing an English translation of that; simultaneously, Rogers and son have done an updated English version which Zondervan will publish.
I hope I got some of that straight - I am typing this in from memory without checking my sources.
At any rate, I plan to evaluate these two editions when they come out, and will probably mention them on the site then.
Jonathan