While it is certainly the largest super massive black hole found to date, it does have company.
Scientists Discover 'Monster' Supermassive Black Holes
What I find interesting is that I am unable to find out how far away they think SDSS J1106+1939 is from us. Since we are talking about a quasar/ULIRG, I am going to presume that it is more than 7 billion light years away (redshift z>0.09).
The distance is important in understanding how these super massive black holes form. In the example above of the 10 billion solar mass super massive black hole, it was only 2.7 billion years old by the time we saw it. Which means that it had to bulk up fairly quickly, and is probably considerably larger today, 11 billion years later.
If SDSS J1106+1939 is also about 11 billion light years away, then the super massive black hole would have had to bulk up faster than we had previously anticipated. If SDSS J1106+1939 is closer than 11 billion light years away, then there may be a limiting rate at which super massive black holes bulk up. Either way, knowing its approximate distance is important information.