Ever needed to make a new PDF containing a subset of the pages of an existing PDF?
The pdfnup tool is nominally for printing PDFs n-up (n logical pages to a sheet), but it can be told to cut and paste pages into a new PDF, like so:
pdfnup original.pdf --nup 1x1 --pages 1,3,5,7,21-25 --outfile subset.pdf
On Ubuntu, you can install pdfnup with a simple sudo aptitude install pdfjam.
Further reading: pdfjam
Update: pdftk also seems like an intriguing option, especially for more complex operations.