Just to offer a dissenting opinion I want to relate my short story.

I interviewed for my current job kilted, and bearded. Almost didnt get it. I interviewed at the corporate office though the job was going to be on location, not there. My interviewer (who is also my direct boss and works on site with me) didnt have much problem with the kilt, but the head honchos of the company did.

In the industry I work in we wear uniforms, so really I feel whatever you wear on your own time is irrelevant. However we also do contract work, working at the site of our clients and so there are multiple sets of sensibilities to be considered.
Also, the position I am in is very much all about image. In fact I would say without a respectable and commanding image our job is impossible to do correctly.
I was fortunate that the person I interviewed with recognized my talents despite the kilt, and had just enough pull to get his decision approved despite anyone elses opinions.

Its all worked out well now. I not only got the job I was hired for, but got a promotion two weeks later, and am now being trained to take over the whole site soon. I'm very happy with my job and really pleased I got it. The kilt could have stood in the way of that.

Ultimately my point is not that wearing a kilt to interviews is bad. (If I leave this job, I'll probably interview kilted again) Its just that you need to understand what exactly the kilt means to you.
At one time I was totally into the kilt, as the kilt (and this is even just for modern kilts - I still dont have a traditional tartan)
Now its just clothes. It doesnt have any more important meaning other than something to wear which is both comfortable and practical.
I would have no problem trading in my jeans and t-shirt for slacks and a dress shirt when interviewing, and I dont think there should be a problem trading the kilt in either.
It isnt a betrayal of who you are or what the kilt is, its just a concession to reality. The reality is a job interview is a chance to sell yourself, and as any marketing grad will tell you packaging is important.