Same here; the YKs on my keychain take an incredible amount of abuse, rubbing against keys and other objects all day long, for years, and I've never had any trouble. Contacts don't show appreciable wear (and they've had thousands of insertions).

One thing I'd really, really like is for a way to distinguish multiple YKs. The things are so durable that they won't take a permanent marker, and I've had to gouge identifiers on them, clip off corners and so forth.