I would love to see a characterization of this bug's impact. Reading the description, it doesn't seem to be nearly as serious as the author of this post is making it out to be. But there's no information about how fast the client will step up the transmit rate after a period of quiescence and no data from traffic analysis to determine how frequently real-world servers encounter this condition and the overall effect in terms of dropped packets, increased queue depths, and latency spikes.
(Google are actually in a good position to provide these data; a number of Google's own services will doubtless benefit. I suspect the scale of Google's operations means that even a barely-measurable decrease in latency or queue depth compounds to a big gain pretty quickly.)
Strictly speaking, it can't be too bad, since it would immediately stand out if Linux boxes have decreased network performance in a mixed shop. Maybe a few percent in the average case, with maybe some specialized applications more affected.
(Google are actually in a good position to provide these data; a number of Google's own services will doubtless benefit. I suspect the scale of Google's operations means that even a barely-measurable decrease in latency or queue depth compounds to a big gain pretty quickly.)