I do not believe that we know the answer to this question for sure. I personally do not believe that computers negatively affect students' intellectual growth.
People who think that computers are bad believe that the internet makes it too easy for students to plagiarize or to at least borrow others' ideas without thinking for themselves. I do not agree that this is true. I think that students who really care can use the information they find on the internet to help them think through issues, not as a way of avoiding thought. There will surely be students who do use computers and the internet to avoid thinking, but those are students who wouldn't be doing much thinking even if the internet weren't around.
If the question refers to mental growth, then the answer is no. Children today have the world at their fingertips, and are able to access it by typing a few words. There is a social component to the Internet that concerns me, though. Students have become lazy and have more difficulty with face to face interaction at times due to the ease with which they can "chat" with someone from afar. They also spend so little time doing active things.
I think there is a definite change in the way students learn now, but to characterize it as negative would disregard all the amazing opportunities the computer age has brought us.