Not counting spambots, probably around 5. Maybe a bit more, but not much. I'm pretty lenient and it takes a lot to get me to ban you, you must have really screwed up if you do make it that far.
I have probably only had to hand out around 1-5 bans. On my own site I was known as the Evil and Kind administrator, spammers saw the "evil" side and I didn't tolerate them while I was a lovely and friendly administrator to those who are loyal and good members.
In general not including spambots, the amount of users banned depends on the size and maturity of your community, this often has something to do with niche.