Pretty often, especially in the realm of journalism (Wikileaks et al) and especially in network-security journalism. (Imagine writing exposés about botnet-owners. Imagine what kind of DDoS results from that.)
Yes and Amazon is the company to go running to if you are doing things that the establishment does not like. I don't think so.
A lot of game servers (eg Minecraft) get DDoSed by competitor servers or players as revenge
More generally: I think a decent fraction of the people who think DDoSing is an appropriate way to deal with personal vendettas are kids. The targets of kids' vendettas are often also kids. Kids tend to have low budgets. (The budget required to launch a DDoS, through one of the many commercial websites that sell them, is pretty low.)
A better question would be, "How often are people on a budget the target of a budget DDOS attack?" I think we've long since entered the era where DDOS attacks don't have to be "serious" to be massive.