I agree with the other comments that it would be 'nice' to warn them (and give them a 1 click unsubscribe)... but most companies (in the UK) allow you to sign up to free trials online but to unsubscribe you have to call them.

I presume this is because by making the barrier to unsubscribe higher you get fewer people unsubscribe, and probably some people who don't use a service but remain subscribed because they don't notice.

It's also common to require x (where x is 28?) advance notification for unsubscribing, so even when you do so you usually end up paying for another month anyway.

Some services (e.g. The Times Online) give you a free (or reduced price) trial, after which you agree to a 12 / 18 month subscription. This seems even more evil, but I guess they do it because it 'works' and they're about making money rather than being nice.