Illusory security is terrible and is worse than no security
One of the possible responses to my entry on how your entire download infrastructure should be using HTTPS is to say more or less 'well, at least the current insecure approach is trying, surely that's better than ignoring the whole issue'. My answer is simple: no, it's not. The current situation covered in my entry is actually worse than not having any PGP signatures (and perhaps SHA1 hashes) at all.
In general, illusory security is worse than no security because in practice, illusory security fools people and so lulls them into a false sense of security. I'm pretty sure that almost everyone who does anything at all is going to read the Joyent page, faithfully follow the directions, and conclude that they're secure. As we know, all of their checking actually means almost nothing. In fact I'm pretty sure that the Joyent people who set up that page felt that it creates security.
What makes no security better than illusory security is that it's honest. If Joyent just said 'download this tarball from this HTTP URL', everyone would have the same effective security but anyone who was worried about it would know immediately that they have a problem. No one would be getting a false sense of security; instead they would have an honest sense of a lack of security.
It follows that if you're setting up security, it's very important to get it right. If you're not confident that you've got it right, the best thing you can do is shut up about it and not say anything. Do as much as you can to not lead people into a false sense of security, because almost all of them will follow you if you do.
(Of course this is easier said than done. Most people set out to create good security instead of illusory security, so there's a natural tendency to belive that you've succeeded.)
PS: Let me beat the really security-aware people to the punch by noting that an attacker can always insert false claims of security even if you leave them out yourself; since you don't have security, your lack of claims of it is delivered insecurely and so is subject to alteration. It's my view that such alterations are likely to be more dangerous for the attacker over the long term for various reasons. (If all they need is a short-term win, well, you're up the creek. Welcome to security, land of justified paranoia.)