I previously was experimenting with the -d feature like this:

RewriteCond $1 !-d RewriteRule RewriteRule ^([^\./]+)/(.*) /$1.php/$2 [L]

But for some reason it didn't work. %{REQUEST_FILENAME} instead seems to be the right think to look at.

my own experience about 1 or 2 years earlier was mixed. I was also using Multiviews with Apache1.3 and we did have 406s by some Googlebots but regular 200s by other Googlebots. My conclusion was, that the bots they have running are slightly different software or different versions. All I know is our content was accessible in the Google-Index, but wether it took longer or had other sideeffects - I didn't investigate/compare back then. But it's probably best to avoid it alltogether.

Good to know, that there is a solution for Apache2. Thanks.

As for a general mod_rewrite solution - textpattern uses the following which I find pretty nice:

RewriteCond %{REQUEST_FILENAME} -f [OR]

RewriteCond %{REQUEST_FILENAME} -d

RewriteRule ^(.+) - [PT,L]

RewriteRule ^(.*) index.php

REQUEST_FILENAME is the full local filesystem path to the file or script matching the request.

-f checks wether it is a file.

-d checks wether it is a directory.

If either is true do nothing (-) and skip the remaining rules (L). The last rule rewrites everything to index.php but can easily be replaces with your rule above:

RewriteRule ^([^\.]+)$ /$1.php [L]

(In case the comment form ate up the code, here is a link: http://svn.textpattern.com/current/.htaccess )