I think it's traders in general. I know it's used by US equities traders. I think it was referenced as being used in the LIBOR manipulation scandal, as well.
Yahoo Finance and Sports are still very popular around the globe, and Yahoo Japan is among the top few websites visited in the country.
There are still a few Yahoo! Groups I'm a part of that are resistent to moving on to greener pastures (such as Groups.io). That and Flickr (which will be free of Yahoo! soon enough) are the only two reasons I still have an account.
I've had my Yahoo mail account forever and I still use it. It's my public facing email account, which will receive very few important things, and no one I actually know uses it to contact me.
I still use Yahoo mail. Happy user since 1990something. I use gmail as well, but I consider it inferior. They both have problems, but at least Yahoo mail's problems are consistent.
Yahoo Auction is also still very popular in Japan.