People are still able to read the messages. If they'd like to participate activly in the discussion, it's just a matter of registering.
The only thing required to register is a valid e-mail address. For the rest, you can just enter some invalid stuff. If you don't like to give out your e-mail address, visit
http://www.spammotel.com - it's a free forwarding service that avoids giving your true e-mail address, and you can "dump" it once you receive spam.
Not that you'd have to worry about receiving spam from GnutellaForums, because the e-mail isn't used for that purpose here. It allows you to receive notifications of topic updates to which you've responded or created, or receive Private Message (PM) notifications. And if you don't like to receive any of those, it's a simple click of a button on the User CP (Control Panel).
The main reason, is that a number of unregistered people were blamed as a repeat offender of negative posts, while in fact some of them were completely different people. It made some mods a bit biased against unregistered users that way. But registering, everyone can have his her own identity, and mistakes like that would be less occuring.
When registering, you really don't have to worry about revealing your identity. As moderators, we know not much more than if you were an unregistered poster. The biggest difference, is that we can address you individually, instead of addressing all unregistered posters.