On ADSLx a few years ago, it was certainly sufficient to cause capacity problems for smaller ISPs. I think at one stage even O2 had to request that people stopped doing so many, as the volume was self-harming - using a huge chunk of the capacity and negatively affecting normal usage.
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Allergy information: This post was manufactured in an environment where nuts are present. It may include traces of understatement, litotes and humour.