XSL-FO and NFop
To sum up this afternoon of exploring .NET/pdf options, XSL-FO seems like an attractive possibility.
The XSL-FO spec is pretty extensive so it' www.renderx.com, but the opensource alternative is supposed to work aswell (haven't had the time to code a prototype yet).
The .net implementation is called NFop and is a direct port from the Java Fop project at apache.
The advantage with this solution over the ready-to-go solutions like DynamicPDF for .NET and ABCPdf.NET is of course the use of standard way to transform your xml. Hard coding transformations using pdf-conversion object models will create a problem when the customer wants the pdf to look differently.. With XSL-FO he can.
To get started; download the NFop binary from Sourceforge, and check out Laurent Kempé's tutorial (in french, but the source is readable for all).