I stand corrected about groups tackling larger books and even series. There are groups out there taking on series, even of the doorstop variety.
For fantasy readers and book groups I wanted to share my recent discovery. Tor.com has two current threads in which both George R. R. Martin’s Game of Thrones books are being reread and can be found under the A Read of Ice and Fire tag and discussed and in which writer Jo Walton is rereading Patrick Rothfuss’ The Name of the Wind and The Wise Man’s Fear which can be found under the tag Kingkiller Chronicles.
Both of these reread threads and discussions offer rich, detailed fodder for anyone delving into these books.