My Dyson DC04 seems to have lost power in suction when in upright mode.

Simon Tindall, March 2006

This happened to me. So with a little help I stripped it down and cleaned it out. Sucks like new now. But it's a fiddly job.
Full how-to instructions with photos here:
http://www.dyson-online.com/technical_advice.htm
They also sell parts and tools to make the job easier.

Michael, March 2006