Web site idea... chart a number over time

This is a super simple web site idea I had, and wanted to know if anyone else would find such a web site useful.

I often want to keep tabs on something on the internet. How many new subscribers/day on magnatune, or how many backlogged requests there are on my web site, how many google hits there are for the word "magnatune", etc...

So... I was thinking of a super simple site, where you:

- go to chartanumber.com, to create a daily chart
- indicate a url to fetch and a text pattern to use to extract the number you're interested in
- the web site then fetches that number daily and makes the chart for you on demand.

Useful?

This seemed like something I could personally use, and maybe others could too.

There are a bunch of chart-creation widgets out there -- I could potentially let you choose which one you like best (i.e., google charts, a flash-based widget, etc...)

I haven't found anything like this on the internet. Do you know of anything like it?

-john