First of all, the plugin is AMAZING! Thank you so much for coding it.
I have found one problem: I have product descriptions in Spanish, with accented characters, like "Tú". When you reach the Paypal page, the encoding of these words is broken.
And one question: In the sidebar cart, why does the title appear twice, when you add products to the cart? i.e. there's the sidebar widget title and the shopping cart title.
Let me know if you want me to contribute my Spanish translation of the plugin (only the public area so far).