IMPORTANT: Backing up your wallet does not mean that you will be able to easily reuse the wallet with the new app instance. It means that you will be able to recover your funds with use of external entities like myetherwallet. If you want to make a backup with reuse of the current ethereum address please backup whole golem app and store files in a safe place.
Your Golem wallet stores GNT and ETH for use on the network. We highly recommend that you backup your wallet when you begin to use your Golem app. That way if your computer crashes and you cannot recover your files, you have the keys to your wallet to recover your funds.
Your wallet keys can be found in your app directory. The locations of the app directories for each supported OS are below:
These directories contain everything associated with your Golem account and the app itself. The exact location of the wallet keys are inside those directories under:
Copy your keys from that file directory onto a piece of paper and store in a safe place. You can also back these files up to another hard drive if you wish, but the safest way to store this data is to write it down (just remember where you put it!).