   Saving textures in RAM
  My 2D game loads some images (texture objects) from files and some from the framebuffer. Do texture objects ever use the pixel rectangles stored in the RAM? After loading the textures to the GPU, is it safe to delete them from the memory? It is clear that textures loaded with glCopyTexImage2D() don't use RAM, but I'm not sure about other textures. If they are kept in the GPU (even if in normal memory, not necessarily high performance texture memory) I can delete them from the RAM. And save a lot of memory.   
  Yes, once it's uploaded to the GPU, you can delete your copy.  The GPU has it's own memory manager/organizer that will put it where it needs it (either GPU memory, or main memory), but it will create/store it's own copy, so once you load it, delete it and stop wasting memory ;).   ;http://www.opengl.org/wiki/Texture_Mappingand more specificallyhttp://www.opengl.org/wiki/Texture_Mapping#Texture_Storage