After months of working, finally BackTrack 5R1 is now released to public. According to the announcement, this version uses Linux Kernel 18.104.22.168 and it has gained 30 new tools on this release along with regular 120 bug fixes and 70 tool updates.
There are several flavours available for you to download: Gnome and KDE ISO images for 32 and 64 bit, as well as a VMWare image of a 32 bit Gnome install, with VMWare Tools pre-installed.
You can start downloading the ISO and VMWare image on their download page, but for now, only Torrents are available even though they said HTTP mirrors should be ready on August 20. I'm in the process of downloading the ISOs and Image on UKDW's ISO Server.