Edited by Frederic G. Cassidy and Joan Houston Hall, 1985 (vol. 1) - 2011 (vol. 5). Intensely complete, with many items recorded in no other well-known reference. For example, last night I was reading Barbara Kingsolver's The Lacuna, and came across dincher. It's not in OED2, MW2, MW3, RHD2, CDC1, Urban Dictionary or Wordnik (till now). DARE has it (under dinch): a cigarette butt. See the DARE website for more info.
Last word: check back in 2011, the work hasn't been completed yet.