FYI,
APART from driving in the rain (to me the only thing that really matters with directional tires), I ran and raced all kinds of tires in both directions and had no issues whatsoever. The tires gripped just as hard in one direction or the other. Some people even drive on tires incorreclty mounted without even knowing... (hell some people drive on poorly inflated tires without any issue, well at least for the lucky ones!).

Anyway, I believe the direction really only matters in the rain (water doesn't get pushed out correctly through the grooves). Noise will likely be increased as well, and wear possibly accelerated to some degree.

That said, I would not run tires against what the manufacturer recommends unless I have a good reason to do so. Not driving in the rain could be one, or knowing that you can't go that fast then.

But be responsible and follow what the manufacturer directions say, not what you hear on forums!

All that said, it would be nice to hear if someone with incorreclty mounted tires had a bad driving experience as a result.