As one of the editors of the PG online catalog, I believe that the two projects can be very complimentary. Wikipedia articles can benefit from having appropriate book-length items mentioned; Project Gutenberg can benefit by having encyclopedia-type articles for authors in the collection readily available. 

 ::I add reciprocal links between the two when I happen to come across them. There is one wikipedian —  — who is gradually working through the PG catalog and notifying me of author links to add to the PG catalog. However, this is rather a time-consuming task, and anyone who would like to help (perhaps by checking authors alphabetized under one particular letter) would be most welcome.