for a given fund to be able to specify the date you joined and perhaps how much cash or how many units you have in the fund. The percentages would then tell you how much gain or loss you made so far. (and could include reinvested distributions + further purchases as well)

It would be cool to get a percentage, or profit across a portfolio of funds.

I'm doing this already just in excel.

just tried to upload an xls file and got told invalid file.

Apart from that the graphs on this website look really great and load really quickly using ie7 running on vista 64 ultimate.