nina asked:
What was your experience with it, is it a popular tool? I downloaded it for the free 30 day trial… If not, what do you use?
What was your experience with it, is it a popular tool? I downloaded it for the free 30 day trial… If not, what do you use?

All tools are pretty subjective. They all have their own 'databases'
To determine which keywords rank best for my particular site, I used both wordtracker and keyworddiscovery. I also used Google Adwords. All three had different results, so I selected keywords on a combination of the three tools. This site helped me out too: it has an article on selecting the right keywords.
My favorite keyword tool is WordTracker.com. As part of their subscription service, which isn't exactly cheap, you get quite a few useful tools. But they do have a free trial that you can use as many times as you want, and many people often find that the free tool suits their needs. Theres also a free keyword tool at SEO Book that i've found to be quite helpful and accurate.