[lierduh]

Each time the script is run.

1) It re-generates all the sitemaps. Makes sense because you have more threads/posts now.

2) It notifies Google about new sitemaps being available. You will notice Google fetches these files soon afterwards.

If you have the scheduled task logged. The end of the log is the response sent by Google. It should say:

======================
Sitemap Notification Received

Your Sitemap has been successfully added to our list of Sitemaps to crawl. If this is the first time you are notifying Google about this Sitemap, please add it via http://www.google.com/webmasters/sitemaps so you can track its status. Please note that we do not add all submitted URLs to our index, and we cannot make any predictions or guarantees about when or if they will appear.
======================

One thing to remember is under your Google sitemap account. The 'last submitted' does not reflect the auto ping/submit. It only logs the manual submit you do by push the button at Google sitemap account.

Other search engine do not accept sitemaps as far as I know, at least not using Google's sitemap format. The redirects however works for all the major search engine which I believe benefits the indexing.

I do not recommend using SEO at least for existing sites. The chances are Google has already indexed part of your forums using links like /showthread.php?t=12345. Now if you rewrite all the URLs, Google will have two copies of the same contents for that thread. (one with the traditional URL, one from your new rewrite URL). This will lead Google panalizing your site ranking. Some smarter SEO scheme redirect your old URL to the new one does not suffer this, but it becomes a very complicated add-on. It may break every time a mojor vB version is released. I elect not to use such scheme. For the record, I used URL rewrite SEO back in vB2 era. In my .htaccess, I still need to redirect my old rewritten vB2 URLs in fear of Google penalizing my site. Basically the vB archive is very static, it was designed for SEO in the first place anyway. Think about how many clickable links a normal showthread brings to you, it becomes a mess for search engines no matter how smart your SEO is.

For index.php redirect, my working version is:

RewriteEngine on

#...

RewriteCond %{QUERY_STRING} ^$
RewriteRule ^index.php$ / [R=301,L]

If it does not work for you, I would check the http logs. Failing that, log your rewrite! (you need to do this in your http.conf, consult apache manual for log level etc.)