IMHO Seam-PDF is very useful for quickly knocking up basic PDFs. As soon as you start to do anything too advanced (or pretty) then you need to dive into the iText API and write your PDF generation as a Bean.
Personally I prefer using PDF templates as you can get a designer to knock up something that looks ace. In the absence of a designer you could always hack around in Adobe Illustrator like me and get something that looks like my cat threw up on it.
We had designers throw together the reports in iReport and then had a Seam component that would compile and service report requests. It did require a bit of extra work because we had to use non JDBC data sources to expose our Seam components to the reports. However, it did give us some flexibility with report design that we couldn't get with the seam-pdf.
Seam-pdf and Jasper are also both based on iText so in theory anything you can do in Jasper you can do in Seam-pdf.