ShaperProbe is a research tool from a team at Georgia Tech that detects and characterizes "traffic shaping" by ISPs, determining which US ISPs deliberately slow down their customers' traffic, and in what way they do so. They've published a paper on their findings, which indicate that cable ISPs do much more "shaping" than telcos, with Comcast and Cox being the most aggressive, even slowing down the traffic you send, in addition to the traffic you receive. Georgia Tech researchers recently demonstrated another tool, Kermit, which also measures ISP performance. Both projects were funded by grants from Google, who have a clear interest in helping Internet users determine which ISPs practice throttling and shaping (notwithstanding Google's Net Neutrality sellout with Verizon).
The use of shapers can also be dictated by the underlaying access tech. The researchers note that DSL providers can "dynamically change link capacity instead of shaping, while a cable provider is more likely to shape since DOCSIS provides fixed access capabilities." It can also be applied to the entire Internet link or more narrowly to specific kinds of traffic– which, as the researchers note, is "relevant to the 'heated' network neutrality debate."
The research shows that Comcast, Road Runner (from Time Warner Cable), and Cox all use downstream shaping–but only Comcast and Cox also use upstream shaping. Neither AT&T nor Verizon shape in either direction.