Between WordPress 1.x and 2.x there was a big change to the way rewrite rules are handled.
In the old days, everything got written out to a <a href="http://httpd.apache.org/docs/1.3/mod/mod_rewrite.html#RewriteRule">.htaccess</a> file. Every condition, every form of permalink could be found there, and I had some comfort knowing I could see and mess with it all. I was a bit surprised to find that with 2.0.2, WP writes out a sparse file that has only one significant rule. Something that looks like this:
RewriteRule . /blog/index.php [L]
That one line takes everything in your request URL and passes it through to index.php for processing. The beauty of this is that WP doesn’t need to write to the file system with every change to the permalink structure (which used to include every new “page” added or renamed).
The only downside to this is that you can no longer expect a $_REQUEST array full of all the query terms your plugin might use. Instead you’ll have to use the <a href="http://codex.wordpress.org/Function_Reference/WP_Query">$wp_query</a> object. All of this was probably mentioned in the API docs before I built a bunch of dependancies on $_REQUEST, but it was easy enough to fix.