HTTP_REFERER variable

how reliable is the $ENV{HTTP_REFERER} variable? i noticed that a good number of feeds providers use this variable, as well as some sites' members area and some leased content areas. this is also used in .htaccess to prevent hotlinking.

However, i've noticed that this variable can get lost easily (especially with AOL customers on proxy servers)....and can be spoofed very easily.

my question is: do you use this variable? if so..for what? and how reliable is it to depend on this value?

thanks,
hagan

If the variable that I am thinking about is the same as the ASP, I think that it is only valuable on the previous link as well?