Does anyone has any number showing this mod is actually working for their site? i.e it improves SEO enough to warrant adding more stuff to your site?
You have to understand what it does, in that it records the one-off visits we all get to a page on usually relevant keyword phrases, but due to someone that has searched through pages of websites and clicked on the listing. The phrase is then recorded on the page in a specific area (cloud) and next time Google spiders the page, they find the exact keyword phrase that say was on page 5 of Google before, and suddenly it moves up the pages, usually landing on the first page of Google results.
The way it works is by usually increasing the priority and using heading tags even, to highlight phrases that are finding that page more than another, so it gives them priority by visit numbers...
Via the ACP, you can delete non-relevant terms that people find a page on... and this helps reduce your bounce rate, which can be counter productive to this mods purpose if not managed. Sure, you may capture more traffic, but you water down your overall pages purpose and worth by keeping non-relevant phrases around, so you delete / ban them from the ACP from ever showing again. Basically, an ignore feature for a word/phrase so it doesn't keep hindering the overall page purpose / site purpose.
If Google keep delivering traffic to your page from non-relevant terms, that is their issue, not yours... as long as you don't abuse it, I have found it extremely beneficial in picking up relevant members who may not otherwise of found your forum.