It is very unlikely that the homebrew channel alone would brick your wii, but anything is possible. Your brick is going to come from further softmodding and almost always from doing something you should not have done. If you read and understand the guide presented here they are very safe. But sh*t happes, power goes out, net goes down, these things will brick your wii if they happen at the wrong time during softmodding. So if you are not will to risk your wii for the added features, don't do it. But I think most people would agree that the benefits are worth the risk involved.