One more note on my above comment, like Pinterest, it's clearly written in the WordPress.com TOS that if you reblog something to your WordPress.com site, if the original copyright owner takes legal action, it will be directed at the member who reblogged it, not WordPress.com.
Jan, the Pinterest sharing button on WordPress.com that everyone was asking for and which was made available is optional. You don't have to use it in your site unless you want to. Obviously, those that clamored for having the Pinterest share button are not the same people who want to have Pinterest blocked, unless they've changed their minds.
The Pinterest "Pin It" bookmarklet is, for all intents and purposes, "Press This". It was only after Pinterest became a tsunami that they released the meta tag that allows site owners to block others from using the "Pin It" bookmarklet on their site and pinning their material. I can only hope that WordPress.com will give us the option in our settings, especially since sites like flickr have already done so.
For now, like reblogging, either you learn to live with it or you go someplace where you can include the meta tag in your site's header info.