permalinks without index.php

Don’t use permalinks without anything numerical, since your site may be broken! I use /post-id/postname. Something with css files that cannot be found and I can tell you from experience: you don’t want that!

Using only %postname%
If you use postname as the only element in your permalinks to create a structure such as example.com/post-title, the rewrite rules may make it impossible to access pages such as your stylesheet (which has a similar format) or the /wp-admin/ folder [is this true in WordPress 2.0+ versions?]. It’s best to include some numeric data (e.g. the post ID or date) in the permalink to prevent this from happening. Additionally, WordPress v1.2.x requires the use of a date structure in order for some features, such as the calendar, to function properly. /%year%/%monthnum%/%day%/%postname%/ is always a good start.

It’s still in the codex.

I had the very problem described and the worst part is, is that the admin no longer works either. I “backspaced” back and solved the problem, but in that time somebody on the forum closed his/her browser or something and that’s when the fun starts. My advice since is: walk the save way or at least be warned (you notice instantly when things go wrong and only then you can change it back). I’m not sure if this still applies to recent versions of WP, but since it’s still in the codex, I’m not going to try!