I have been an extremely early adopter of DemandTools and other products by Validity. (Think first year they started!) It is one of the first screens I open each day. It has saved me countless hours in working with data. It is the on product I encourage every SFDC Admin or data user to check out.
Yes, I have migrated over. It took me a little bit as I had so many scenarios saved over the years of use. I do find myself jumping between the two sometimes if I need a long forgotten scenario!