In my experience driver give me a lot more room and I haven't had any negative comments yet. I use it in flashing mode during the day and have been told by drivers who passed me (we were on the same course, I commuted in by bike) that they thought the light was a good thing as it really brought attention to the bike.
I have ridden behind my wife, who uses my old DiNotte 140L, and not found it a problem...
Ps. I now use the DiNotte 400L rear light, which is visible at about 1 mile in full sun light...