It seems that we're understanding each other. :-)

> yes there does seem to be an issue here. I snipped the "generation 0" 
> part of that image did File | Save As...
>  then reopened the new version and repeated the save several times.
> There is continual degradation. This should not happen with an 
> identical image. This seems to suggest that either there is a bug in 
> the compression or that the decompression is not producing an 
> identical image from the stored data.

The explaination from Øyvind K. clarifies exactly what I'm going 
through, and his proposal makes sense for me.
Photoshop always shows a "save as"-like dialog when you save a JPEG from 
the camera for the first time, letting you adjust the compression.
If I press CTRL+S in Gimp, it saves the file and destroys it.
That's where de difference is.

Please, keep in mind that I'm not asking to turn Gimp into a Photoshop 
clone. I've changed not for the money, but for the freedom. So save the 
"Gimp != PS" stuff. I know it and I'm ok with that. :)
(BTW... after a couple of months with Gimp, when I go back to PS I 
totally hate it. I haven't CMYK but I have other things that I love. I 
had to make a sign of 30.000 x 11.000 pixels with lots of layers and 
Gimp worked fine, while Photoshop choked).

Back to the topic: I propose to display the quality settings when an 
image is resaved as jpeg for the first time, if it's possible.
I don't know how it's done, but when I take my image to PS from my 
camera, it asks me to adjust the quality when I press CTRL+S for the 
first time.
After that it saves normally.

I repeat: Now I understand the scale used in gimp for the quality. I 
know that jpeg is a lossy format and my camera uses it and it destroys 
image data because of that, I always knew that, but that's not my 
problem here.
My only issue now is the first save of a jpeg from the camera without 
changing the quality (using just CTRL+S) recompresses too much the image.
The first time I open the image (directly from the camera) it doesn't 
look over compressed. If I save it, it is recompressed too agressively 
(or at least it looks like that).
Nothing warns me it will happen, it just happens and I don't know why.
I made the comparison with PS because it doesn't happen there. Just 
like a reference.

Thank you for your time!

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