As noted above the Dyson does lose suction when the cyclone below the filter gets clogged. This clogging may be the result of using the Dyson for vacuuming fine construction dust as it was for me. The Dyson is not shop vac. I am thinking it is because it does not have a bag filter and is more susceptible to clogging with fine dust. While initially frustrating, this turned out to be an easily solvable problem. In addition to cleaning the filter you have to take apart and clean the cyclone unit. To be conservative, I would not use water to wash it out as it is not designed to be cleaned in that fashion and it is not necessary. Take the cyclone outside, wipe it, shake it and blow it out with an air compressor or one of those aerosol cans. It should only take a few minutes. I now use a shop vac to clean those construction projects around the house.
FYI, March 2010