Anonymizing the key IDs doesn't offer extra protection in some cases. For example, if you send a message to a vendor, or an email to someone on TorMail, anyone with access to the SR or TorMail servers knows who the recipient is, so there's no reason to hide the key IDs from them. However, I can think of cases where it is useful. A vendor may want to send an encrypted announcement to several customers, but he doesn't want them to know who the others are. That's as much for their protection as his. The recipients would only be able to deduce the number of other recipients, but they couldn't compare the key IDs to people in their key chain. Another example is if someone gains access to your computer, but not your TorMail account. Let's say you saved encrypted messages in a text file, as a back up. Then the attacker would only know how many messages you sent, but not who the recipients are. BTW, if you think you can only be charged for physical drugs in your possession, you should review the Farmers Market case. They were charged for a lot of shit that they talked about in their Hushmail accounts, and that was the only evidence of those crimes. An email counts as a confession.