If you are gonna be able to make donations for mounts/gear etc I think you should add a way for people to see if the item was donated for or acquired legit.
If you are able to donate for awesome gear, then there is no value in getting it yourself and destroys the purpose of this game completely.
My suggestion is where the "heroic" mark on gear is, have something like "donation" or something like this.
We won't enable donor bashing or excluding players who have donated from some guilds, raids, etc. If you don't think that this would happen, trust me, we all know that it would. It already happens as it is.