Summernats is something that needs to be experienced at least once in your life if you are into cars / being a rev head. It is a festival centered around cars - mainly Australian and American V8 cars. It is one of the best known car festivals in Australia, and it generates interest and revenue in Canberra - a dull city for most parts of the year. It also brings in a somewhat drunken exhibitionist type of person to the city, but this is a small disadvantage of the festival.
The Canberra Times recently published an article about how Summernats could be hosted in Canberra for another 25 years. It is also interesting to read some of the shallow and narrow mindedness of some of the commenters, who claim to live around Canberra when Summernats is on. They have said they do not want Summernats in Canberra - "Too much bad behaviour. Not good for the environment. Bad, noisy, bad..."
As mentioned, Summernats, for all its bad points, actually gives Canberra something to look forward to for the year. I will admit there are some other festivals as well, like Floriade, but nothing is to the same scale as Summernats. If Canberrians do not like Summernats, then I suggest they move away from Canberra. Try Karumba - population < 1000, on the beach, but then again they would find something to complain about that. Stop making Canberra duller!