I wrote a battery laptop monitor : http://batterybarpro.com . I get about 1k uniques a day and net about $1500/mn in sales of the Pro version.
How do you get the word out on a utility like this?
I started with a free version that I posted on various freeware software sites and as many forums about laptops as I could find. I also watched referral URLs can tried to engage users. Eventually users started spreading the word themselves. I've tried AdWords a few times but the ROI hasn't been great.