I had my DRLs activated for really just one reason: I don't much care to use 'flash-to-pass' and I'm hoping the DRLs will make me more noticable to slower drivers in the left lane as I approach and they'll move over without having to resort to using flash-to-pass.
If they don't move over now (with the DRLs on), I kind of figure they're not going to move over if I flash-to-pass, either, so I just pass them on the right when the opportunity presents itself.
It's mainly just a courtesy thing. I try to avoid flying up upon a slower driver so as to give them ample time to change lanes and, with the DRLs, I'm hoping that it will make me that much more noticable as I approach.
'03 330Ci: Topaz Blue/Black 'ette, SP, Bi-X, HS, MR
'02 Mazda MPV: Coastal Blue