[bojan]

Jeremy,
I fully understand why you never needed to clean the sensor.
But my case is somewhat different from yours...

Let me summarise:

With Canon DSLR's, dust on sensor is cleanded by means of ultrasonic tranducer that "shakes" the dust from IR filter (Canon cameras have that system, I don't know about others but I imagine they have something similar). The simplest camera modification (that I have done it myslef) includes removal of IR filter and consequently, ultrasonic cleaning system with it.
Dust on sensor is not a big problem when lower f/numbers are used.
And, dust specks are not a big problem if hystograms are stretched only slightly (if at all).

As I mentioned in my post, I only needed to clean the sensor (2 times in two years) after I modified my Canon 450D camera (by removing IR filter, so ultrasnic "shaker" was also removed), and because dust specks become much more visible ("focussed") starting with f/5,6 and up (this is because the sensor glass lid is closer to sensor than IR filter.. at f/10 (C11, MTO100A and Rubinar-1100) they are quite sharp, and when adjusting curves in postprocessing (that means increasing contrast, gamma and excessive stretching is applied) dust specks are also significantly enhaced, sometimes even when fresh flats are properly applied.
And, as last one, I do not want to pay for cleaning service, because I do not run a business.. so I can't justify the cost of professional cleaning service (to my better half.. especially because she knows I know how to do it... ).