First of all, sorry for the long rant..Mods, please take it to the feedback if this deemed fit there..
I just recently noticed about 3 dust specks on my sensor. They were quite prominent right in the middle of the sensor. Though they were appearing only in a clear sky or low contrast pictures, I felt uneasy about it and gave it a clean with Giottos Rocket blower. Unfortunately it didn't help much and as Thom Hogan says, it was more like a welded dust which required a wet clean. I had an event in my office in the office to shoot and I was nearby Nikon Service Centre in the morning for a meeting. I thought I'd give it to Nikon this time for a proper clean.
Guess what? I was briefed that the Cleaning is chargeable and I agreed to pay the $26.75 including GST. The Camera was taken in and brought back to me within 20 mins. I looked through the viewfinder and the viewfinder had 3 to 4 very prominent specks. Then I asked the engineer for a gray card or a pure white card to focus and shoot. The answer came back as Nikon doesn't have them and worse yesterday's sky was hazy and dark. The glass window through which you can focus the sky was filled with dust as well.
I took an A4 sized paper and focussed it at infinity with F22 and the sensor now had about 6 -7 specks instead of the initial 3. The engineer apologized and brought back the camera in for cleaning and came back with the viewfinder filled with dust (more than 40 specks).
To cut the long story short, the engineer cleaned the sensor and the viewfinder focus screen 7 times and every time it was worse than before. And by the 7th time he got it back to me, I asked him why is it that every time when you clean the dust is increased in 10 folds. Then the engineer said that Nikon Singapore doesn't have a clean room and Nikon never guarantees that the sensor will be dust free after the cleaning.
I gave up at this time and asked him to return the camera. The camera was tested again with the A4 Sheet and there were very tiny dust specks. The engineer then asked me, why are you shooting at F22 as they will not be visible in wider aperture. I was almost furious but kept my cool and said that it's the way I ensure that my sensor is dust free.
I came back to my office and the sky had cleared up a bit. I gave a test shot and again, it was back to square one with 3 specks but on the top left corner instead of the mid screen. I called up Nikon again and the same engineer was brought on line and he asked me to bring the camera back for cleaning at FOC. I politely rejected it and said that I'm traveling and I have no time to come for another 7 to 8 sessions of cleaning.
I've to go to Cathay later tonight to pick up the sensor swabs and E2 as I'm flying off tomorrow morning.
My piece of advise to everyone here, if you think Nikon does a better job than you in cleaning, good luck to you all..