[development] Question on base_path() in hook_init and caching

I've been recently struggling with getting my cas module to support caching (not agressive caching). I started by getting error messages when I called arg() in my hook_init and am now having problems with base_path() not being defined. Can anyone suggest a strategy for eliminating these errors? Is there a bootstrap function I should be calling in my hook_init? If not should I be filing a core bug related to this, or should I not be able to use arg and base_path in a hook_init function? Thanks for any help Dave