For the staff mastery, as Sanni_shaiya said, it affects the cooling time between 'instant' skills, so if you were using Magic Arrow, instead of cast----cast----cast, it would become cast--cast--cast with staff mastery.
If a skill takes 3 secs to cast though, it will still take 3 secs. Skills with a set recharge time will also not be affected I think, though they may recharge a split second faster - skill recharge appears to be made up of the stated recharge time, and a recharge time based on attack speed (total recharge time = stated recharge time on the skill + attack speed recharge time). It is the recharge time based on attack speed Staff Mastery will affect.
As for mounts, I may be wrong, but the ap only mounts are the only ones able to be traded I believe (except the razormares, garamoths and the 'slow' snowboard), oh and the Xmas goats can be traded. Their cost runs into the 'Ops' (far more expensive than you will be able to find on the ah boards). Atm a lvl 50hm light mount ranges from 2ops to 4 (Silverhorn for eg). The Xmas mounts are also about 2-4 ops. I think the 58um mounts are a little more expensive. When mounts are not being sold, their price goes up, and when there are mounts in the web item mall (say, in a teir), prices go down (intuitive neh
). Based on how many mounts you see for sale in tc, work out what you think you can sell your mount for.