We bought a house recently and got our air ducts cleaned this week. Great service overall. No mess was left behind and there were no hidden fees, the price was what was promised on the phone.
Note: if you are very sensitive to smells, the smell of disinfectant is quite strong for the next 24 hours or so. Also, the vacuums they used were quite loud, so if you have little ones or pets, you might want to take them out of the house.
It's awesome to have fresh air to breath! Mike told me that the ducts were probably never cleaned before (20 years, gross). That said, once the cleaning is done there is no need for cleaning for the next 5-7 years.
Again, thank you Top Hatter for great service!