Previously it was the "Serious Pony Discussion Forum."
Probably just a drunken whimsy of Jeph's. Before that it was the Sexy-Dad's Discussion Forum (for just one day), and I don't recall what before that.
EDIT - Here is a full list of the forum titles over the years, with approximate start dates (my favourite was "Suddenly: BUTTERFLIES"):
2005, Mar 5: Questionable Content
2008, Mar 8: OH GOD THE PAIN
2008, Apr 1: FURIOUS MASTURBA [gunshots]
2008, Apr 7: Rock Out to the Piched Toms
2008, Apr 16: whaaaaaaaaaaaat
2008, May 18: BONER WARS
2008, June 21: I DON'T THINK THIS IS VERY FUNNY
2008, June 28: Forums Admin Password: BUTTS_1980
2008, July 1: bloodbloodbloodbloodbloodbloodbloodbl
2008, July 7: A Ass Pocket of Whiskey
2008, July 10: Girl Versus Boy Versus Whale Dicks
2008, July 21: My Fursona is a Leech
2008, Aug 22: Suddenly: BUTTERFLIES
2008, Oct 12: QC Talky Place
2009, Feb 26: SexyDads Forum*
2009, Feb 27: Serious Pony Discussion Forum
2010, Dec 7: PonyLeaks Discussion Forum & Sex Furnace
* From memory - I can't locate a copy with the full title (the first word is exact, though)
March 2008 is around the time that Jeph started to get really fed up with the forums, and from Mar 2009 he became nearly inactive in them. The Dec 2010 change followed the storm that appeared in this forum around the breakup. This quote shows Jeph's mood at the start of the changes:
The temptation to just destroy everything I have ever created has never been higher.
In October 2011 I changed the title to the current: QC & Ponyleaks Discussion Forum
This was to keep a link to the past while moving towards normality.
In June 2013 I finally reverted the title to simply: QC Discussion Forum