Here is a list of HP/Linux references:
Amazon: Mix of HP-UX and Linux solutions as related on http://www.zdnetindia.com/techzone/linuxcentre/stories/42345.html.
Checkpoint: HP Secure OS for Linux (aka Trusted linux).
Boeing: Linux and HP clusters help Boeing R&D reduce costs as related on http://www.hp.com/products1/linux/infolibrary/boeing.html.
ViaWest: a hp/Linux ISP as related on http://www.hp.com/products1/linux/infolibrary/viawest.html.
Israel Aircraft Industry: a hp/Linux performance cluster user as related on http://www.hp.com/products1/linux/infolibrary/israel.html.
SpeedEra: a hp/Linux ISP as related on http://www.hp.com/products1/linux/infolibrary/speedera.html.
Dreamworks: The Shreck movie realised on HP netserver/Linux as related on http://www.zdnet.com/zdnn/stories/news/0,4586,2761566,00.html.