This wishlist bug is still up to date. The MMAP patch by Phil Wood is now updated against 0.9.8, the current Debian version, and as documented in his page improves performance on high speed network interfaces for all software using libpcacp (most sniffers). A hands-on experience of this is reported, for example, at http://eatingsecurity.blogspot.com/2007/09/transparent-bridging-mmap-pcap-and.html