WordPress MU

New to Wordpress MU. Been going through activating themes. But I'm confused as to this language int eh documentation:
"In particular, compatibility with Widgets is important as users cannot edit themes. Each theme used is shared by all members using that theme. If you make a blog-specific edit to a theme, ALL blogs using the theme will show it."

I just logged onto to a test blog account, and I could move around widgets, adjust that themes settings, etc. A couple of questions:
1) If i make those changes to that theme, i.e. place a widget in a sidebar, does that happen to every blog using that theme?
2) if so, how do you turn it off so only the admin can make those changes?

Thanks so much!
JOhn

No, the widgets are blog specific. Placing a widget in a sidebar isn't changing the php in the theme itself.

they work exactly like wp.com does.

(I can go rework that codex page)

2) if so, how do you turn it off so only the admin can make those changes?

Modify the theme(s) to use the "the_widget()" function to define what widgets will be used by default when the theme is activated. Then use one of the available plugins that let you modify the dashboard menus to hide the Widgets menu from your users.

Thanks both andrea_r and kgraeme! This makes more sense now. But one more item:
If a theme has customizable options (like color options or insert logo) those won't change the php right so individual blogs would be able to use those customizable options?

That's kind of the point of those options pages. :) Those are stored in the db, they don't affect the php of the theme.

Again, look at how wp.com does it. They have themes with options pages for this very reason.