Question for people using these progress bars: Are you actually doing the computation to accurately estimate the time it takes to complete the action indicated by the progress bar, or are you simply showing a progress bar as a visual cue to any loading in the same way people have been using spinning AJAX loaders?
compu-what-tion? You mean accurately predict how long it'll take an ajax request to load? Pfft, an exercise in futility, easier to just fake it, and probably just as accurate :)
Using these super thin bars as a "dumb" loader seems like it would only confuse your users. It's like using an icon other than the floppy disk to convey saving.