I've been searching the forums and faqs and tried all the samples. GUISkin doesn't work. I tried creating a guiskin (twice!), dropping it on an empty or the camera (but it won't let me edit it in the inspector for those objects but seems to list it, but won't let me select one (shows Assets as empty when you click to bring up Assets within inspector for a change).
And I tried GUI.skin = myguiskin in a script that is assigned to both an empty and a camera (just to confirm). The controls are created but the skin is never applied.
I also tried doing a custom style and yes, that works per assigned control(but unfortunately wipes out the borders, etc. that you get with the default, so isn't pretty, and doesn't seem an easy solution unless you are doing to do a lot of very customized, non-scalable GUI controls.)
[the above with custom styles might be expected behavior, I don't know, since the example tutorials in the docs don't seem to show much in the way of textures (usually just text without any background). and I don't know what to expect for guiskin since it won't come up at all.]
So it makes me wonder if it's only available if you have Pro?
I have latest free edition of Unity and haven't reached the point of needing Pro yet.
Thanks so much for any insight (and again, I've tried all the samples and read all the docs, and searched the forums, but nothing works and no one clearly states if this is Pro only ability)...
Where it says "None (GUISkin)" you can click the circle at the end of the line and assign the skin in the inspector that way. Sounds like that is your issue. You can also drag it onto the text "None (GUISkin)" and it will highlight the area with a blue before you drop it.
Alternately you can do the following:
You need to create a folder in your assets folder named "Resources", and then put the GUISkin you created in there. Also, change the "MyGUISkin" to match the name of the GUISkin file you created.