Mr Optimistic,
Seeing as Mike-Bracknell has decided to play the "bad cop" role and beat you up over saying yes to Automatic Updates, I reckon I'd better inject some balance.
Firstly, you should be congratulated for saying yes to one too many automatic updates. Better to have too many updates than too few !
Secondly, I think it might be a good idea to ask you the reason behind your original question. What are you trying to achieve ?
Finally, in relation to what software requires .NET .... to be honest, if you've already got it installed on your computer, you might as well just keep updating .NET ..... will be quicker, easier and less painful for you than trying to track down what software is using it, looking into whether you need that software, uninstalling that software etc. etc. etc.