So I did some digging because 1) I'm going crazy waiting for the Back to School sale and the new MBA and 2) I'm super bored.
Follows are the dates in the last 6 years of when the Back to School promotion began.
2011 - June 16th (Thursday)
2010 - May 25th (Tuesday)
2009 - May 27th (Wednesday)
2008 - June 3rd (Tuesday)
2007 - June 5th (Tuesday)
2006 - June 5th (Monday)
Next are the dates in the last 7 years of when WWDC was held.
2012 - June 11th (Monday)
2011 - June 6th (Monday)
2010 - June 7th (Monday)
2009 - June 8th (Monday)
2008 - June 9th (Monday)
2007 - June 11th (Monday)
2006 - August 7th (Monday)
While there may not be any sort of correlation between WWDC and the Back to School sale, I think it's particularly interesting that the Back to School sale consistently began before WWDC. In 2010, it began 13 days before WWDC. In 2009, 12 days. In 2008, 6 days. 2007, 6 days. And 2006, almost 2 months (let's just call this a statistical anomaly). However, in 2011, it began 10 days after WWDC.
Also, within the last 6 years, the B2S promo has always began early in the week (except 2011). So it's possible we see it come tomorrow (Wednesday), but more likely than not, in the upcoming weeks on a Tuesday {not so sure anymore}
I'd also peg it for coming sooner than later, if you go by the trends at least. I'm not sure if the release of Mountain Lion really has much to do with the B2S promo