The biggest reason for me to use the brower detection is the fact that Opera did not support javascript very well before 7 and I just did not have an old version on my computer. I will download the old verisons and see where things die, if at all.
This is what feature detection is for. For example, say Opera 7 lacks the getElementById() function. You can, as you have done, check to see if the user is running Opera 7, and if so not use getElementById(). That's browser detection, which is what you have done. The problem is that some other browsers might also lack getElementById(). So, instead, you should use a test statement such as the following:
Code:
if(typeof document.getElementById === "function") {
  // ... getElementById()-requiring code...
}
This is known as feature detection, and is a much better idea.