feature request: better statistics manipulation

Hi, I often tag apps and websites with more than one tag. For example, all websites I tag "Internet". Some of these are useful ones, so for example, they're relevant to activity X, so I tag them "X" as well. Others are relevant to activity Y, so I also tag those as "Y". I have applications not tagged as "Internet", but that are tagged as "X" and "Y". I'd like to be able to see, out of all the hours that I spend on the Internet, how much of it was spent doing X things, which I can then call useful Internetting, as opposed to just surfing.