Just FYI. The folks at Google have added an integrated Task Management program to gMail (it's in Labs, go there and click on it to enable).
It's a basic sort of thing. No categories, but you can have as many Lists as you want, so you can have a list for @Calls, @Office, etc. It is very easy to make an email a Task and you can indent items for a outline-like list. Also, each task has a Notes field that you can use to hold data, next steps, etc.