You'll find here in the US that the average, non-kilt wearing citizen does not even know what tartan is. They use the word "plaid" for it consistantly, and mostly when applied to flannel shirts.

Those that are invovled in Scottish-American activities are more likely to know what a tartan is, but use the term pretty much only to refer to named Scottish clan or district tartans. Often I'll hear a comment (referring to a non-named tartan) such as, "Oh, that's not a real tartan, it's just a plaid."

Obviously, either use of the term plaid is incorrect. But those who actually take the time to learn about tartan traditions quickly learn the true story -- and forums like this are part of the educational process!

Aye,
Matt