I just had quite a scare. I noticed an unknown script in the source of many of my websites.
At the beginning it had added:
<script src="http://1.2.3.4/bmi-int-js/bmi.js" language="javascript">script>
And at the end:
<script language="javascript"><!-- bmi_SafeAddOnload(bmi_load,"bmi_orig_img",0);//-->
My first idea was that either my server or connection was compromised, but it is actually part of the HTTP accelerator used by my UMTS/3G provider (KPN Mobiel Internet) to save traffic.
So there is probably nothing to worry about. 
well, in half-common cases it will reduce traffic…
however, it will reduce the image quality, and if you decide to view in original quality,
it will cost you more bandwidth than without it. (extra payment for the ISP, ka-ching!)
in other word it forced-low-quality measures.
another trouble if you encounter sites that employ with anti image leeching mechanism,
you’ll not able to view their images, normal quality or reduced otherwise.
not to mention it quite slow (that also more payment if you’re using time based scheme with your ISP),
the reason is theres more ‘user’ accessing its reduced-quality image server, than normal user accessing the original image hosting sites, so expect your image loading get even more, and more slower in the future.