I don't know much about Google toolbar, but if it's sending the entire URL to Google that's almost certainly an offense under RIPA.
Anything in a URL after the first single slash (technically, anything beyond that which is necessary to identify the machine the webpage is on, but it's usually considered to be anything after the first slash) is regarded as content, and making content available to others, ie Google, is interception.
And you can't "opt-in", for the same reasons a Phorm opt-in wouldn't be legal. For interception by consent the express permission of both parties, ie the user and the website, is needed.
Google ain't getting my permission to look at URL's for my website.
It's past time for an "evil Google" smilie option on el Reg methinks. Gates and Jobs have them, why not Google?