I noticed amillar's diary entry about hiding your home on GPS tracks so thought I'd mention a script I wrote to process GPX files:

http://public.subversion.nexusuk.org/projects/kismet-tools/trunk/gpx_trim.py

This lets you specify bounding boxes - any track segments starting or ending in the bounding boxes will be trimmed to remove the bits contained in the box. If the track just goes through the bounding box instead of starting/ending in it, it is left as-is.