Michael Calore of Wired News writes about a coworker who called their ISP, RCN, after having trouble sharing a file using BitTorrent. Instead of being told that RCN was blocking his ability to seed torrent transfers, he was scolded for being a copyright infringer. Most instructive was this graphic of ISPs known to hobble BitTorrent traffic, taken from the Azureus wiki site. Though the chart notes that such information is mainly conjecture (since actual blocking is hard to verify), it appears there is a long list of providers who might be taking steps to limit BitTorrent traffic specifically, or high-volume users generally.
Of course, there is a way to fool ISPs: packet encryption. TorrentFreak points out that both Azureus and uTorrent support some form of encryption to obfuscate exactly what kind of packets you’re sending and receiving from your machine. So if you want to beat “traffic shaping,” it might be a good time to look into taking countermeasures.