Unfortunately, apparently still no support for plug-ins?
And the vaguely suggested help for developers... marginal: "built-in web developer tools to debug, tweak and optimize a website for peak performance and compatibility"
As far as plug-ins go, Safari's had them for years. Apple just doesn't support them or advertise them.
Safari has supported plugins since before I got my first Mac. I use Inquisitor for searching right now. Google SafariStand if you don't believe me.
Mac users who want to block ads can get GlimmerBlocker, which blocks ads on every browser at once. If you want to customize Safari further, GreaseKit allows you to inject your own code into sites (it's Greasemonkey).
Apple won't do anything further. In their mind a program should be designed with the right features in mind up front, and then everything else can be hacked for the people who really, really care. Most of the people who use Safari like that a lot. I do.
I don't want StumbleUpon. I don't want Snap Previews. I don't want del.icio.us or a music player plugin or whatever else plugins offer. I want a browser that lets me access the web as powerfully as possible. The only plugins I care about are the ones who make that more efficient.
"WebKit–Based Plug-ins"
This is how ClickToFlash works.