I wanted to share this with the rest of you, many of whom are like me and relatively new to digital SLRs. It's common knowledge that dust is an issue when it lands on the sensor, so I try not to change lenses constantly or open the shutter and stare into the thing the way I did with my film cameras.
Attached are a few pics that show what dust might look like in your camera. The first two are before/after crops (1" exposure, out of focus, directed at a white wall). The third is the result of overlaying the before and after images in Photoshop, blending the layers using the difference option (i.e. mathematically subtracting one from the other), and then tweaking the curves to amplify the result. Ignore the noise and vignetting, the dark blobs are where the dust particles were before cleaning. This picture isn't cropped so it shows the relative size of the blobs--not small are they? It's worth noting however, that these were rarely visible in most of my photographs... it's when I had large areas of even tones, like with a sky, that they're objectionable.
Okay... the main reason for my post: a recommendation. If you don't have one already, get a Giottos Rocket or Q-Ball blower! It's not exactly a technological breakthrough, it's just the right tool for the job. It actually provides a real blast of air unlike those tiny blower-brushes. Even more clever is that it has check valves that allow fresh air to enter the bulb only from the rear so it doesn't suck in the dust you just blew off from inside your camera. The last thing I want to do is touch the sensor in my camera with any thing or any chemical, so I'm relieved the Q-Ball worked as well as it did.
http://www.giottos.com/before dusting
after dusting
difference
...and how about an actual photograph? Just one more reason I love my wide angle lens!