Roughly how much space does 1 hour of HD video take up?
Thats a hard questions to answer b/c 'HD' can be 720P or 1080P. Also, depends one what codec is used to compress the video or if its uncompressed.
But with a quick google search I found this (quoted from the site I found):
Be aware though that the space a video will take up varies from each recording because video quality may vary slightly. Also each recording may contain more information, for example compare a recording of a black screen will take up less space than a recording of a sports event.
* HDTV = 12Mbps (5.4GB/hr) - 18Mbps (8.1GB/hr)
* SDTV = 4.4Mbps (2.0GB/hr) - 6.7Mbps (3.0GB/hr)
* DVD = 3.5Mbps (1.6GB/hr) - 6.0Mbps (2.7GB/hr)
* MP3 = 128kbps (57.6MB/hr) - 256kbps (115.2MB/hr)