I've read on a forum that after a new camera is launched one should wait about 6 months before buying it, because the it'll wear out the "novelty price" and it won't get much cheaper after that. Is it true?
I'm planning to buy a Nikon D3100.
If cost is your biggest concern, the best time to buy a model of camera is when the next one comes out. Then you can purchase the 'old' model at a discount, or even better, buy gently used from those that are desperate for the new model. This requires patience and self-control, which among us camera geeks, can be in short supply as it relates to camera gear.
This works with cars too ;)
If this is your first serious camera, you should not wait. You're just delaying actually learning about photography and making photographs. That lost time is worth a lot more than any potential price-drop savings.
If you already have a good camera, when something fits your needs, you should buy then, not before or after.
One month before you need it. That way you have time to learn and get accustomed to it by the time you have to use it.
Like most electronics, the price of cameras rarely goes up because technology is still constantly improving. So, buying it later, is not a risk.
However, the price of lenses (other than the most low-end ones) does go up by a good percentage every few years. So buy your good glass early... plus you'll get better image quality.
Like anything in the electronics world, it depends on how much you want/need it. If you are a pro, needing the best gear, then maybe you should buy it right away. If you don't have to have the best, then maybe wait a while. If you buy something now, it will only decrease in value later, but that won't change the good worth you can get out of it now. However, I will warn you, the price drop for new cameras is only about 25% per year, so it might not do as much good as you think it will. So, simply put, buy it if you need it, wait or re-consider if you don't.
This certainly wasn't the case with my camera. I guess it also depends on the camera, brand, geographic location, whether you buy online, etc. Here in Canada I bought my Canon kit at a retailer for $1250 in December of 2010 with an extra complimentary battery. 9 months later the same camera without the battery is still $1250.