i did in April the incatrail what was an amazing experiance , i did with peruplanet a local agency in cusco they gave me the official (no commercial ) website for the incatrail where you can find out how manny spaces are still left on the incatrail
for the moment are many days full till july
so control yourself iff you like to do the trail
http://www.inc-cusco.gob.pe/frame/index_consultas.php