Thunderbird has got extremely fast pdf viewer built in. I think it would be a good idea to make it standalone application. Becouse there are not so many free and fast pdf viewer applications. Adobe and Foxit are big and slow like elephant. Good applications like PDF-Xchange Viewer, PDFLite are discountinued. There's only Sumatra PDF application, very fast and open source project. So, I think there is a space on market for another ultra light pdf viewer.