You've got 800+ mb of apps and data installed on the internal SD. The .android_secure file is well, a backup of the entire .android_secure folder. When you go to Manage Apps and tell the phone to "move to SD card" (some apps just install there on their own) this is where they go.
My backups are about the same size as yours but I've got like 102 apps installed, and quite a few are 20+ mb games.
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