"Substantial" is relative, of course. Here's Bloomberg:
Democratic challenger Mark Begich leads by 814 votes in his bid to oust incumbent Alaska Senator Ted Stevens, according to the state's elections division.
Alaska is still counting absentee ballots from the Nov. 4 election. Anchorage Mayor Begich had been trailing Stevens by 3,257 votes until state officials started counting approximately 90,000 absentee ballots yesterday... Officials counted approximately 50,000 ballots yesterday and may finish counting the remaining 40,000 tomorrow.
The upshot? The Dems could be up to 58 Senate seats as early as tomorrow.
Update: More info from AKMuckraker:
As we move forward, Alaska's "reddest" areas have already been counted. Those outstanding districts are mainly rural and tend to go Democratic. Friday will see more than 20,000 "question ballots" (provisional ballots) counted, and the remaining absentee ballots are slated to be counted Monday.
So nothing is final yet, but the news is definitely good.