I found this page being discussed in another forum and thought it may be of interest here ->
http://pixinfo.com/en/articles/ccd-dust-removal/
To save a bit of reading, conclusion copied below.
Dust removal conclusion
Here is our ranking according to effectiveness: - Olympus: good
- Canon: poor (we are disappointed)
- Pentax and Sony: useless (we are very disappointed)
If you are looking for a camera, have the dust removal as an expectation only at the end of your list. If sensor cleaning / dust removal is a must, the choices are limited to Olympus and Panasonic cameras.
We guess that theoretically it is possible to get better results with Canon cameras when the CMOS sensor is not charged, but Canon must find a way to discharge the sensor first (if this is really the problem). If the system is so unreliable, the EOS-ICS is not much more than a good marketing name.
In case of Sony, Pentax and Samsung cameras, the dust removal function should be considered as almost non-existent.
The final conclusion: keep your air blower handy, it is still your best tool against dust.