Email is great. A valuable business tool. But I do hate it when conversations you have with it suddenly don't become 'private'.
Obviously nothing in email is secret. It's incredibly easy to reply to people, cc a few others into it and before you know it. lots of people can see what's been written. In the 'old days', that wouldn't have happened as much.
As an example, there is something on my 'to do' list - but it is a low priority. The manager who wants me to do the task has emailed me about when it will be done - and 'cc'd' my manager into it. It wouldn't have hurt to simply email me - rather than 'cc' my manager in . I don't have a particularly good relationship with my manager at the moment.
I can think of other 'email' chains - where people have been 'cc'd' in - yet really they don't need to know. Incidents could have been resolved with simple talking to people - or just directly involving people in emails - rather than people just getting one side of a story.
Maybe I am being a bit sensitive - but I do think that sometimes 'cc' in an email chain is used against people.