Let's say A wants to find B's IP address. In the case of email, A would need to trick B into replying to an email (and also use an email service that adds the client IP header). In the case of most IM servces, B would need to accept a friend request federated from a server. If I'm understanding this correctly, with Skype, A merely has to query B's status to get B's IP address.

In the case of email, the easiest way to get a user's IP is to have them load an external image.

Not true if you use a secure/intelligent email client, like Gmail. It will prompt you with a yellow bar above the email before loading any images.

It also implies that they'll open the email, which most average people won't do unless they know the sender or are otherwise expecting an email.

It's scary when you think about the context - someone you haven't added to your contact list, meaning anyone at any time, can find your current IP.

It's not exactly shocking, but it certainly shouldn't be able to happen until you've approved a person as a contact.