From the archives...
http://www.independent.co.uk/news/w...n-bounce-gives-gore-lead-in-polls-711712.html
August 2000, not much of a lead but decent.
Also have a look at this for reference.
http://upload.wikimedia.org/wikiped...he_use_of_going_through_with_the_Election.JPG
That's not much of a lead and it also only measures the popular vote, which isn't what really counts in the US, e.g. extra votes in California won't help Obama much. There's also the Bradley effect to take into account in this case but I still think it'd take something fairly major for Obama to lose at this stage, its far from impossible though.