The AndroidMarketArchiver helps you keep a record of your App's statistics data as presented in Android Market developer console.
It logs into the Market Developer Website on your behalf and grabs a snapshot of the relevant data.
For getting a data snapshot call
./grab.sh <your Google Account> <your Google Password>
(The script is just a wrapper around a java call, so should be easily portable to shell-free platforms.)
The script is set up for a market console with one app, use -apps <number> in grab.sh if you have multiple apps in the market.