Naturally the answer is 'it depends.' What does it depend on? What you plan on doing with your camera. To take @che's example, often times newsguys treat their lenses and camera bodies like crap because they know that the pictures they take are often going to be printed in black and white and at a crap resolution anyway. The dust is never gonna show up or noticed!
Similarly, the photog who spends more of their time playing around with really wide open apertures, dust just isn't as big of a problem as it becomes when you're working with really small apertures. Ditto for photographers who mostly work in the studio. My primary work is as a portrait photographer and I manage to get around to doing some dust cleanup in my camera body about once every other month...
Those who spend more time outside, or in heavy weather have more to worry about, but even so I think we tend to baby our equipment more than we need to. I was chatting with a Canon rep at a seminar late last year and he talked about the filter that protects the sensor being 'quite a bit more robust' (his words) and scratch resistant than people give them credit for (especially in cameras that have come out over the last 2 or 3 years). His recommended method for cleaning was wrapping a microfiber cloth around the end of a pencil, rubberbanding it on there, and swiping around inside the camera to clean it out. This is from an official Canon guy. He went ahead and demonstrated on a 5DmkII that he had on the table!
I don't know if I'd go as far as to recommend that DIY of a method, but I do think that in general it is easy to implement a cleaning protocol that doesn't involve paying a lot of money to have your camera sent out to be cleaned. There are a couple companies such as Visible Dust which market 'safe' cleaning solutions. I use Visible Dust products since I got my Canon 20D about 6 years ago and have never had a problem...