Legato technique specialist Allen Hinds gives an incredible insight into this way of playing in the 14 pages of exercises and licks that come with this "A Lesson In Legato", his first for JGS.
Allen talks about his technique openly. He starts with the single string legato exercise you've probably seen before. Starting on the 3rd string: 9-5-7-9-7-5. He then takes this motive everywhere. All the examples have been meticulously transcribed. These transcriptions make it easy to follow the wealth of information Allen is providing.
There's also a part about incorporating slides into your playing.
In between the exercises we get a lot of info about Allen's background. Cool the way he talks about Allan Holdsworth.