The question and the answers given never fail to amuse me.
For as many " I BG bot 24/7 for 5 years I never get banned blah blah blah" there are just as many "I Dl HB for the first time today clicked start and got banned blah blah blah"
The simple truth is what we do is against Blizzards TOS, you risk a ban every single time you start the Bot regardless of what you are having it do. It just takes one player report, one GM looking too closely, or any other of a hundred things and bye bye account.
If you need an example, I have a couple of accounts that I have only BG botted on for a little over a year, no warnings nothing. I have another a few months back that had been sitting for about a year, I decided to fire it up and PVP gear up my Rogue. Started the Bot, BG que popped I watched it initiate and then went to get a drink and came back to a Disconnect screen and a Ban email. Its luck of the draw my friends.
I do believe that some things are more prone than others though, and my own personal opinion is that GB2, and BG bot are very high on my no no list right now, but at the end of the day Don't bot what you can't lose. It's like speeding, the more you do it the more likely you will eventually get caught.