I've seen several of these letters and all but one were all from opennap. The other was from WinmX PNP but this was awhile ago. Seems the RIAA targeted some of WinMX's supernodes for a short time but it's been kinda quiet lately. If this keeps up programs/protocals like Filetopia and Freenet which are encrypted and anonymous will become the next wave of the P2P community. Freenet is developing rather slow though
Opennap is just too vulnerable for the RIAA's prying eyes