This is a pet peeve of mine, the number of times I've seen a band reffered to as Post Metal when they clearly arent is a bit annoying (sorry, but its the pedant in me). Recently I've seen Agalloch, band who's music is based in Black Metal, described as Post and before that Grayceon, who are best described as "god alone knows".
For those that dont know, Experimental is more of a catch all genre for bands that wouldnt fit into tech/extreme or prog metal which explains the lack of a clear deffinition and why bands with seemingly no similarities are lumped togethor (think In the Woods... and Grayceon).
Post Metal tends to be based around using the riffs to develop textures in the music through layering and repitition. The primary bands that have, and continue to, define this genre would be Isis, Neurosis, Pelican, Cult of Luna, Mouth of the Architect, Rosetta, Minsk, The Mourningside, Baroness, The Ocean, Giant Squid and Jesu. Obviously you get groups that step out of this mold whilst still keeping Post Metal feel, most notably The Pax Cecilia. That probably sounds like a pretty useless description to some, but I hope the list of bands gives a clear indication of what Post Metal is.
Edit: Prog Geo has reminded me of an important point that I missed. The reason these two are lumped together, other than the fact that Post Metal is really just a bit too small to exist as a seperate sub genre on its own (there's probably only about 40-50 bands listed here, maybe a few more) is that theres a strong conection between the style of a lot of the bands we have here classed as Experimental and Post Metal plus, Post Metal originally grew out of Neurosis and Isis experimenting with Hardcore and Sludg Metal.
I hope I've cleared up some confusion, though knowing my luck I've just created more.
Edited by sleeper - January 10 2011 at 18:26