As it was meantioned in the Harding thread, the eagle feathers (and ANY feathers that look like such) have VERY specific meanings and significance.
They're traditionally golden eagle feathers, with one being worn by an armiger, two by a chieftain, & three by the clan chief.
It would be "bad taste" to wear them if you are not the person RIGHTFULLY acknowledged to do so with the clan/heraldic regalia.
In Britain, it can even be a criminally punishable offense (under the "identity theft" idea).

In many cases, the ones who have the "rights" (legal recognition through Lord Lyon) to the feathers CHOOSE NOT to wear them, based on the situation at hand and what the person will be doing. To wear them marks that person with distinction as the representative of his clan and office, as well as of himself. WHATEVER he does wearing feathers reflects upon all of them. When he is "normally" dressed any embarassment is "personal" and reflective of the others in ONLY so much as he/she is recognized. One may also choose to forgo feathers to be incognito, as much as possible.

As for OTHER types of feathers, plumes, and the like. As long as they would NOT be mistaken for eagle feathers, go ahead. Remember, however, that for most modern "Scotiphiles" those feathers may be seen as gaudy, pretentious, and all sorts of other things.
Most Americans don't know the difference either way.

Personally, I would NOT wear anything "feathery" as it does not fit my personal tastes or styles. I also tend to not like gold (only my wedding band, some of my buckles, and the like). Usually my leathers are black and my metals are silver (which is personal tastes).

Now, the Tartan Army is not EXACTLY a group to look to regarding dictates on "proper" kilt or Scottish dress, mores, or fashion. Part of the fun of the Tartan Army is to look as gaudy and stereotypical as POSSIBLE.