The numbers aren't bad, and it's actually nice to see them stable. That's a rare thing. Usually they drop from the premiere - until you get to Nov. Sweeps. So Fringe staying the same is unusual, and most likely a good sign. At the very least, it's showing a solid hardcore audience that will watch the show live no matter where it's placed. And since Fringe is currently in the toughest spot in TVland right now, that means Fringe's TOTAL audience is significantly higher.
And my friend talked to someone she knows at FOX, and the word back from her contact was she "wasn't worried about Fringe". It's not official or anything, but I thought I'd just pass it along. As has been said, FOX's only real concern about Thursdays is improving the spot, and Bones/Fringe is doing that exceptionally.