The Code Project always impresses me with how technically advanced their projects are. Thumbnails of PDFs?! That’s awesome! Now if I could only get it running under *nix… 
The Code Project – Generate Thumbnail Images from PDF Documents – .NET
This article presents VB.NET code to create thumbnail images from a directory of Adobe Acrobat PDF documents.
Its not bad… bit dicky to use in practice and has a bit of a security hole in that it uses the clipboard (bad and hard when running under asp.net), and requires you to have acro pro installed, which is costly. Tall Compnents has a far better solution IMHO for the all important pdf->bmp step – http://www.tallcomponents.com/Default.aspx?id=pdfthumbnail. Its free too. Not sure if it works under mono, can’t find the info on their site.
Wow, that is way better!