I clicked add and github and about half the decline of SF happened before github started, and if anything the decline of SF seemed to be leveling off since GH started. So I'd be inclined to think "no".
One interesting thing to think about is I don't use google searches as a portal into /. SF or GH so this might be a better graph of 1st deriv of noob traffic than actual traffic. Its quite possible SF is still much "larger" than GH, just GH is currently growing faster.
Re:Slashdot alternative in the works
by davidgerard on Monday February 10, 2014 @10:06AM
(#7211407)
It declined before then.
But I notice one project I'm an avid user of (LMMS) just moved from SF to Github ... aaaaand suddenly there's a buttload of extra development work, such that in a few months they went from "nothing going on here" to a 1.0 RC.
Where did all projects go? GitHub?