As far as I know, no one pays attention to that attribute.
ANS used it as part of their transition from the NSFnet, but stopped
using it last fall.
There is documentation for this attribute at:
ftp://ftp.ra.net/routing.arbiter/ripe/ripe-130.txt (US)
ftp://ftp.ripe.net/ripe/docs/ripe-130.txt (Europe)
-Brian