We really need to give kudos to these guys. They have been persistent for years in developing a high quality Scheme, and then taking it to the next level. PLT Scheme is practical in its library design, flexible in its reader, meticulous in its documentation and fast as an execution engine.
Making a language fast and well-documented is a thankless task. It's nothing short of a herculean accomplishment for these guys to come out of left field with such a fantastic offering.
so so so true. Whats doubly impressive is that many of the core active members are full time academics who are able to frame their research so that they can both spend their time improving their PLT/Racket, and framing their work as also being genuinely top notch research!