Inviting the adressbook

It's a slippery slope - it certainly helps getting users to join, but it has implications on privacy and trust. That being said I think that most users will probably see it as a service and not a threat. The thing to notice here is that YC users and techies see the problems with this approach, but normal users don't. They just see the service, not the implications of it. So if you don't abuse it I think there are certainly cases where it makes sense to do.

I wouldn't use it either, but there must be some who do. Otherwise I couldn't explain that you can already buy the feature (e.g. http://www.getmycontacts.com)

Whenever I get auto-generated invitations based on systems like these I delete and ignore them or alternatively tag them as SPAM if I receive them from more than one person.

It leaves me with a very negative impression of the site or service before I have even seen it.

As others have said, normal users don't mind this. However this works best in applications which have an inherent benefit in connecting to a lot of people. So while this may work very well for linkedin and facebook, it may not work too well for say a youtube