Should I update to the 1.8 snapshots of Minecraft or will it corrupt my save file?

Just backup your save file by: (The steps bellow is for Windows running Vista or above)

1. Press the windows logo (bottom left) and in the search type %appdata% press enter
2. Go into the.minecraft folder and then go into the Saves folder
3. Copy your save onto your desktop (or anywhere safe)

There! Now your save is all backed up! And upgrading to a snapshot doesn't ruin your save, well it hasn't for me.