Correct, Grumbler, but evidently I spoke too soon. What was driving this is I want to be able to reference my pages as http://mydomain.us/key1/val1/key2/val2/you/get/the/idea where http://mydomain.us/index.php will process it.
So here's what I arrived at (put inside a virtual server for mydomain.us):
RewriteRule /?$ - [L]
RewriteRule /\? - [L]
RewriteRule /[/.].(php|js|htm)(\?|$) - [NC,L]
RewriteRule .(gif|jpg)$ - [NC,L]
RewriteRule /index.php/ - [NC,L]
RewriteRule (.)$ http://headshot.us/index.php$1 [NS,L]
The way this works is that anything after the (even implied) index.php get stuffed into $_SERVER["PATH_INFO"]. Pretty nifty, huh? There is only one problem which is annoying the heck out of me. Apache does an implicit redirect (rc=302) when it uses that last rule and therefore the browser will show index.php in it's location bar. Awful.