this is a fine plugin, but has slow queries on one of sites we maintain. The site has 300,000 comments and the basic queries in this plugin take 3 seconds. That's too much even if the plugin is caching the output - the new comments just keep on coming and the cache has to be refreshed quite often.
These queries are sorting by comment_date and that takes a lot of time. If I change the sort from comment_date to comment_ID, it takes only 0.01 seconds. That's a huge improvement. When you look at WordPress tables, comment_date is not indexed, but comment_date_gmt is. So sorting by comment_date_gmt also increased performance a lot, queries take 0.01 seconds.
Other problematic query is the one which checks for comment_type to equal trackback or pingback. Comparing these string values is slow, adds 1 extra second on our big DB.
Is this plugin still maintained?