Now, it's only one way of determining how a carb (or protein or fat for
that matter) affects your blood sugar.  I've eaten a ton of pasta in my
life, and one reason I'm on low carb is that a meal of pasta would have me
sitting down because of the blood sugar rush, and pasta cooked al dente is
relatively low on the glycemic index.

No.  Net carbs are total dietary input, not some average effect over
time.  If you want to stay in ketosis, for example, it doesn't matter
how fast the carbs hit the blood as long as the liver sees enough of
them over time to surpass it's depletion rate.

Low glycemic does mean that you can clump your carbs together more
without as much of an insulin swing - i.e. less hungry two hours
later.  Also, some folks are only concerned with insulin levels; a
more moderate change means lower peaks.