I've just noted that .Net users seem to have created a load of tags like "2.0", "3.5", "4.0". This seems to me to be a bad idea, (though I realise that some .Net programmers believe that SO was created for them alone) and they should all be retagged as .Net2.0 etc. and the creation of numeric tags be banned in future.
A quick look through the questions tagged
As Bill said, the questions would have to be manually separated in most cases.
I created a Data Explorer query to find all the numeric-only tags in the system and the question count for each.
It doesn't look that bad to clean up. Basically go through each one, retag the ones that don't belong to a major group (i.e., .NET), and then get a mod to merge the rest. There aren't very many popular groups in the list, which is nice.
I think each tag can be put into a different tag that's not numeric only, i.e.