Linden Lab recently announced new Third Party Viewer policy changes, forbidding developers from creating a version of an SL viewer that "changes the way elements of Second Life are defined or how they behave, in such a way that users on other Viewers don't experience the same virtual reality." In other words, these policies are meant to insure that the metaverse maintains the same underlying objective reality that is perceivable by all SL users, no matter what viewer they're using. So for example, the Imprudence/Kokua viewer (which I still use, since it's more reliable for me than the official viewer) maintains much of SL's old school user interface, which is fine by this new new policy. But a viewer which, say, depicted avatars as being nude (which another notorious third party viewer once did), would presumably run afoul. Some TPV developers and fans have speculated that the policy change is directed at particular viewers, but when I asked Linden Lab about that, spokesman Peter Gray said not so:
"[T]he changes to the policy weren't made in response to any specific third part viewer," he told me. Read about all the changes here.
UPDATE, 5:50PM: In Comments, Missy Restless says my example isn't a good one, and offers one of her own. "I think that is the problem with 'shared experience'," notes Hitomi Tiponi. "Unless it is officially defined with clear examples, everyone will have a different interpretation."
UPDATE 2, 11;40pm: Philosophy question for SLers: If a tree falls in the virtual forest and your third party viewer doesn't play audio properly, does it make a sound?