Would you be comfortable with restricting how much information you share with the service and just keeping it around as a utility? Also,.would "deleting your account" actually take away the information they already have?
I was comfortable sharing my information with Facebook back in 2007. But as time has gone on I have become more cynical of their collection and use of personal data. I think this opinion was formed based on individual incidents (opening it up to search engines, changing of privacy settings) and largely uninformed media hype. Over the same period, I have become increasingly aware of my online 'footprint'. I want to get into politics later in life and don't want my opinions/photos/data being taken out of context in the future. Therefore, I prefer social media where my real identity is not disclosed.
Yeah, I never use twitter mostly because of format issues but I've got our just in case it comes in handy somehow.