Not even 12 hours ago Jon Jones was installed as a significant favorite against Lyoto Machida. That line became obsolete once Machida turned down the title shot, and in stepped Vitor Belfort to return to light-heavyweight and get an immediate crack at Jones' belt. The early betting lines are in and Jones is currently one of the biggest betting favorites in UFC history (via BestFightOdds).
The current -900 line, which will change over time -- so the image you see right now will be updated when the lines change -- is the BEST line you can get on Jon Jones. Other gambling sites have Jones listed in four-digit territory and as high as -1500, which is surely the highest for any UFC fight. To put that in perspective, the best line at fight time for B.J. Penn's first fight against Frankie Edgar was -700 and the highest was -1100. Georges St. Pierre's loss to Matt Serra stands as the biggest upset in UFC history with GSP somewhere in the -1000-1300 area in some books and Serra at +700.
If this line stays generally the same come September 22nd and Belfort beats Jones, it'd have to go down as one of the biggest upsets in UFC history along with GSP vs. Serra and Penn vs. Edgar I. Its place in MMA history would also be very high but nothing has ever topped Sokoudjou at +1600 knocking out Antonio Rogerio Nogueira in PRIDE.