How hot or cold is cold e-mailing - there are people who claim to be wildly successful at it and then there are others who simply think its way too outdated and intrusive. Opinions?

Depends on the industry. Say for services like digital marketer where small business owners really get 10 emails every other day for SEO services, your 11th email will make no impact no matter how good copy you write. It can work for some industries though, more like say you cleaned a church in a city and you can cold call other churches in same city and see if they need your janitorial services.