One problem with digital SLR cameras (DSLRs) is that, because their lenses are interchangeable, and unlike "sealed" point and shoot cameras that most people have, they're prone to accumulating dust on their sensors, which can create spots on the images they take. I actually had to return my first DSLR because it came with such spots, rather than developing them slowly over time as is more normal.
In the old days of film, dust wasn't as much of a problem because every time you changed film, you changed the sensor surface. That's also why film cameras could remain useful for decades—you can use modern, higher-tech film in a 50-year-old camera with good results. With digital photography, to upgrade the sensor surface you have to replace the whole camera. That's one reason extremely expensive digital cameras like the Leica M8 are more fetish items than wise purchases.
Anyway, Macworld has a useful article on some tools to help clean dust from DSLR sensors. That includes magnifying loupes, cleaning solutions and brushes, and so on. It's an iffy process that could void your warranty, so it might be wiser to have a dealer do it rather than trying it yourself. I don't need to yet, so we'll see what I decide when that time comes.