Ive been focusing on SEO for the past few weeks. Without touching mod_rewrite - which google has said is no longer necessary ( dynamic urls - those ? and % in your urls) no longer phase the googlebot - The Slurp spider can not read 301 redirects properly, and often times this will cause your rankings in yahoo to drop - so yeah... installing the mod CAN affect your rankings. anyway, without touching mod-rewrite, these are the increases I have seen with google alone.
That is the crawl rate by google.

KB downloaded.
I have also seen an increase in guests from searches - I have seen a dramatic increase in search term relevancy and all this with out an SEO product beyond Zoints Tags.
What did I do? I optimized my Title tag, my meta description and keywords, I made sure all my images had relevant alt tags, and I went forum to forum re-writing their descriptions, making them more descriptive - I thought like someone should think - like a searcher, not as an admin.
I am anticipating even higher jumps over the next 6 months as I produce more content on the front end. The forum will always take care of its self if it is active.
Just my 2 cents.