That is interesting that St. Herman's Press would call him a saint, they were once ROCOR and ROCOR specifically claimed they did not venerate him as a saint. He is listed on an icon as a martyer but ROCOR has said that it was an annoying error. That's in the article on
http://www.orthodoxwiki.org though you said you'd already looked the net.
The controversy is that he, along with Fr. Sergi Bulgakov, were proponants of the theological idea known as Sofiology (not sure of the spelling). Sofia is the divine wisom of God, and has always been thought to be associated with Jesus. For instance, the Church of Hagia Sophia was dedicated to Christ. The Sophiologist wrote that it is a principal of the whole Trinity. One especially controversial point is that it is defined as a female principle. I don't think it was ever declared heretical officially, Fr. Sergi Bulgakov, in fact was put on trial for heresy but was found to be orthodox. He was even defended by his critics, well known theologians like Vladimir Losskey.
So, though Fr. Pavel Florensky did die in the Soviet persecutions of Orthodox Christians, not everyone, maybe hardly anyone, recognizes him as a saint because of some of his writings.
A lot of people misunderstand Sophiology, thinking it is a modern attempt to feminize God. The 'father' of Sophiology was a Russian philosopher named Soloviyev (sp?) who often described it poetically and perhaps went to far. The modern theologian Philip Sherrard was influenced heavily by the idea and explained it very well within the context of Orthodox theology, as did Fr. Sergi Bulgakov. It will remain to be seen if it is accepted or regected, or just falls by the wayside like some other controversial subjects (see the divine name controversy).
Russians find such interesting stuff to argue about. All the Greeks have is the calender.