Convert separate (daily) time reports into one Excel spreadsheet (e.g., for monthly reports)

Usually I report on my daily activities to clients in a following form:

Done today:
1. Done this [2h]
2. Doing that [IN PROGRESS] [3h]

TODO next:
1. Continue doing that
2. Will do one more thing
3. And this too

Problems:
none

I store it for my own purposes in a separate files named something like "report 2011.09.25.txt" in a folders named after a specific client.

* Since reports are sent mostly using email (Dropbox too) it's probably not a bad idea to retrieve those emails as another option apart from local files.

At the end/beginning of the month I send monthly report adn invoice based on that report.
Report is an Excel spreadsheet with four columns and summary at the end. Columns are: Day, Task, Time, Notes.

Since monthly report is only a summary of daily reports, this project has been spawned - to keep everything DRY.