I linked in a site that covers the growing, pruning, and harvesting of raspberries. If you read through it you will notice that raspberries produce fruit on the second year canes which will die after fruiting. That said, harvesting off of canes that produced fruit this year should not overly impact the plant or its fruit production so long as you do not take more than a third of the plant's vegetation off at any time.

I'm sure there are berry or fruit forums were people more knowledgeable about such things could answer.

FataMorgana

Here is a link that might be useful: Growing Raspberries