The fight against digital music piracy seems to always be a step behind the current trends. When the doors were finally shut on Napster, some people * ahem* had already gotten more music via the service in a week than what was on their parent’s entire record collections – combined. People were already starting to use clients like WinMX and Limewire. By the time Limewire was shut down, people had already moved on to uTorrent.

But research published today by the folks at NPD Group suggests a decline in P2P music downloading since the demise of Limewire. According to NPD, Americans downloaded music via P2P client at a 16% clip in Q4 of 2007. In Q4 of 2010, when Limewire went down, that number had fallen to 9%. More statistics from the study:

The average number of music files downloaded from P2P networks also declined from 35 tracks per person in Q4 2007 to just 18 tracks in Q4 2010, although some downloaded just one or two tracks, while others took hundreds. NPD estimates there were 16 million P2P users downloading music in Q4 2010, which is 12 million fewer than in Q4 2007.

“Limewire was so popular for music file trading, and for so long, that its closure has had a powerful and immediate effect on the number of people downloading music files from peer-to-peer services and curtailed the amount being swapped,” said Russ Crupnick, entertainment industry analyst for NPD. “In the past, we’ve noted that hard-core peer-to-peer users would quickly move to other Web sites that offered illegal music file sharing. It will be interesting to see if services like Frostwire and Bittorrent take up the slack left by Limewire, or if peer-to-peer music downloaders instead move on to other modes of acquiring or listening to music.

Yeah, I’m going to go with the find other means option.

After the fall of Limewire, NPR reports an 11% rise in Frostwire use and a 4% rise in uTorrent use. These numbers seem low, especially the uTorrent rise. It might be helpful to note the information was gathered through online surveys. I’m not saying people lie, but people lie. With private tracker torrent sites like waffles.fm and what.cd popping up, people are going to feel more secure in using torrents to download music. (If you can score an invite to one of those sites)

Even with record companies suing for laughable amounts like $75 trillion, for some people that have been freely acquiring all their music since the early days of Napster, it could prove to be an impossible habit to break.