Doesn't support multiple keys with the same name, which is valid and not particularly uncommon. I wouldn't be surprised if it breaks in other ways. This kind of thing is always full of subtle pitfalls.
If you're familiar with Django, this is why the GET, POST and other request dictionaries are actually MultiValueDicts. If you call request.GET.getlist('varname') instead of request.GET['varname'], you'll get a list of each value passed with that name. The brackets aren't special, and if you used them, you'd need request.GET.getlist('varname[]').