All in all, it’s a nice idea to tell people what it means that the service remembers them when logging in. But why on earth have they implemented it modally? Now the dialog covers the Login button and the user is forced to click Okay even if she already knows the message and would like to proceed, ignoring the dialog.
Truth be told, there is a tiny area of the button visible beneath the dialog and clicking it actually works. I’m not sure whether this is an accident or a deliberate design decision, trying to solve the problem with modality. Whatever the reason, I don’t see why the dialog couldn’t be moved to right, leaving the button wholly uncovered.