Migne had become convinced of the power of the press and the sheer value of raw information widely distributed.One can imagine how much he would have contributed to the internet!
His most famous publications were the Patrologia Latina and the Patrolgia Graeca; enormous collections of patristic texts in whatever were the best editions available to him at the time, have not been surpassed in comprehensiveness although over the years, many of the works of the Fathers have been published in better critical editions.
Migne is still the standard for citation of the Fathers. I have spent many happy hours at Wonersh and in Rome, retrieving a volume from the shelves and finding the column number and checking up a reference or reading around to establish the context of a popular quotation. The articles at the beginning of many of the volumes are outstanding studies in their own right.
Private firms have for some time offered Migne for sale or subscription at rather high rates. I have often mused how wonderful it would be if all this information were available online: today I found that the process is well underway. First of all, I found the Apologetic Desktop has well organised links to quite a number of volumes of both the Latin and Greek Patrologiae on google books, as well as other resources that I had not seen online before such as both Lightfoot and Funk's editions of the Apostolic Fathers.
Then I found Documenta Catholica Omnia which links to clean pdfs of the volumes of both Patrolgiae as well as a good collection of other texts. For any theologian this is very exciting news indeed.