I raise this as some years ago I was with a horrible package from Plusnet called "Broadband Plus" with variable traffic management. Essentially, when a user exceeded unpublished limits, Plusnet would throttle all traffic to unpublished speeds. What this meant is that http could be throttled to 128 kbit/sec for exceeding 5 GB usage. The sales literature said "no need to keep track of how much you download" (presumably they thought 128 kbit/s speeds weren't an issue)!. Support staff repeatedly refused to give any kind of usage guidelines to avoid crippling speeds, and customers were locked in for a year.
The heated discussions about this package are still in your forum archive, and the revised product description, which was changed after some pretty bitter arguments, is also in your product archive.
And yes, I accept this was some time ago (end '05 early '06) and Plusnet is a different company these days, but it's not something I'll forget quickly, as it's by far the worst experience I've had with an ISP to date. Some of the same names are still around though, I remember Ben Brown advocating the product.