I am currently listed #1 on Google for my preferred search term. I am also usually listed as the first Adwords ad for that term (not counting Google Base, Ebay, etc.). I'm afraid of a correlation between the two and that lowering my Adwords spending might affect my natural listing. It took over 5 years to get to the top spot.
I figured that was the case but I'm not a SEO Expert or anything and was ecstatic with the organic listing.
If the ad has been running for a while you have a good quality score it means your ad is converting. Conversions with positive ROI is good!