They need to stop ruining the experience for those of us without an account. Everyone was using Twitter as basically an open bulletin board and then they go and make it visitor-hostile. I look at ads either way.
Not saying it's the right way of doing business or that it won't bite them in the butt... but they definitely don't "need" to do it to save the business if the analytics point otherwise.
Twitter seems to have become a cool kids club and now everyone is panicked that someone bought there it was in.