Steve from The Duct Cleaning Specialists spent about four hours thoroughly cleaning out our heating ducts. He was courteous and seemed to do a very thorough job. He also explained to me several aspects of the job before, during, or after it was done. He cut a large hole in the cold air return and four small ones in one of the heating trunks, connected a big indoor vacuum to the furnace and turned it on high - blowing air into my basement from the suction, but it filtered through a huge bag and there was no dust - and then went to each vent and used a blower to blow dust towards him where it was vacuumed with a shop vac, or towards the furnace where the fan picked it up (I'm afraid I don't understand quite how it works, but he showed me a ton of dust so I'm sure it did!)
This is a small, two-man team (Steve and Paul) and my understanding is they get all their business through word-of-mouth, unlike some of the bigger, shadier outfits that mostly do phone marketing.
My only issue is that he sold me (for a mere $5) a filter for my ground floor cold air return, and neither he nor I thought to check that it was big enough, and after he left I discovered it doesn't fit properly. Old houses like mine (1920's) tend to have larger cold air returns than newer ones, and this filter has 1" gaps on either side of the long sides.
Highly recommended, very professional.