It raises an approval screen on the phone. It says

By proceeding, you give another computer access to the following accounts: * [email protected]

STOP! Only proceed if you arrived at this page by scanning a login barcode at google.co. Otherwise, do not proceed!

(start with GMail) (start with iGoogle)

Ah, I see. Thanks for adding that info

There's a bright highlighted warning that says "STOP! Only proceed if you arrived this page by scanning a login barcode at google.com. Otherwise, do not proceed!"

Will users read the warning? I would—and did—it really grabs your attention given the fact its background is yellow and takes up so much of the iPhone screen.

I suppose there are probably other safeguards as well, given that this is Google—maybe timed expiration?

I left the page open and after finished reading comments (a minute or two) in HN, the page gave me this popup dialog:

[Alert] Login session has expired. Press Ok to reload.

This + 2 Factor-Authentication = Pretty Damn Secure.

but those two are different things. They are not complimentry (from what i understand)

I assume it is valid for only a short period like the code generated from the Google Authenticator app.