I run a WP install with around 75,000 posts. I've had these two problems with the plugin:
Very slow updates - update once a week?
I had the "Rebuild sitemap if you change the content of your blog" setting set to true, and every time I updated a post it killed the site. I just realized that was on and turned it off, and voila!
I'd love a feature where it updates on a schedule (daily, weeekly)
Google can't handle more than 50,000 posts. Multiple sitemaps?
I get this error from Google:
Your Sitemap contains too many URLs. Please create multiple Sitemaps with up to 50000 URLs each and submit all Sitemaps.
I'd love it if this plugin automatically created multiple sitemaps (e.g. sitemap2.xml, sitemap3.xml) for a site with 145,000 posts) automatically.
How do I get in contact with the plugin author? My team would either like to (1) make the appropriate donation to get these features built or (2) build out the features and commit to the latest version.