Alright,
I added an option for storing the data in a "log" file.
The log file is a simple csv file with ';' as column separator and "newline" as line separator.

The line format is as follows:
<id>;<date>;<time>;<value>;[dB | Linear]
E.g.:
449;2010-12-10;14:25:00.367;45;dB

The date is in ISO 8601 format.
The time is in "hh:mm:ss.zzz" format as described in http://doc.qt.nokia.com/4.7/qtime.html#toString.

If an already existing file is selected, data is appended to that file.
For the same file the id is continuously incremented during the same vumeter "process".
Consequently, the id is reset if, e.g., a new file is selected or vumeter is closed and restarted.

The newest version (0.10.1) is already in extras-devel.