Dial down the blue, its a little overwhelming.
Use the actual PayPal logo on your site- its available on their site under Tools, adds credibility to your claims.
Pop those buttons with a little more shading and transparency, they look very Windows 95- Google "Metro" and copy from those style sheets.
Left justify your User Agreement. Please. Block high contrast text that is center-justified looks bad, communicates poorly, and is offensive to the the reader. Change it now.
Since your User Agreement absolves you of responsibility for pretty much anything, you should add a clause that you are not responsible for refunds if the world really does come to an end on 12/21/2012. It would suck to go into the afterlife knowing that you owe people money.
That's 5. I'll check back and see if I can help again.