I work as an engineer for a regional ISP in the midwest US.
If we really needed to i'm sure we could but we don't.
Absolutely not. We just don't have the time or manpower to care. Plus your probably not that interesting anyways. Oh and it's definitely against corporate policy, if not also illegal.
Nope. We couldn't care less. We do what we are legally obligated to do by passing on the complaints we receive to customers but that's all. Short of a court order we won't rat you out.
DDoS is the most common. We filter both inbound and outbound. So if your running a DoS attack on someone (intentionally or not), chances are it never left our network anyways. As for downloads I've never heard of anyone getting cut off. I suppose if you use multi-terabytes in a month or constantly choke off the bandwidth for your whole neighborhood though, you'll probably get noticed. I'm sure our AUP allows us the right to disconnect someone for abusing network resources but again i've never seen it enforced.
Intelligence agencies? No. Obviously we can't control what happens to your traffic once it leaves our network edge but we don't cooperate with anyone without a court order.