For me, plaid has two main connotations: the first one being Scotland; the second being school. Scottish influences is the obvious inspiration for the tartan/plaid trend. I don't claim to know much about Scotland but if I think of Scotland I immediately think haggis, bagpipes and of course, kilts. School girl is another possible influence; a plaid skirt being part of a traditional school uniform. College-inspired looks are, as you know, a big trend for this autumn, so plaid will fit in very well.
We've seen plaid down the catwalk before, in many different shapes and with many different slants. The plaid at Alexander McQueen last year caused somewhat of a stir but I personally loved the plaid at Luella (it's pinned firmly to my inspirations board). This season, plaid was back on the catwalk, featuring in Jean Paul Gaultier's Celtic theme.
Plaid or tartan can add a quirky twist to an outfit. Another thing to put on my list of things to try this season.