I use Lantus, Novolog (a fast-acting insulin with a peak at 80 mins),
and just recently added Novolin-R (regular human insulin) to my
arsenal.  Experience with the fast-acting suggests that it usually
works well in small doses (1 - 2 units at a time in my case) to cover
small, high-carb, high-GI snacks or to cover low-carb meals (meats,
vegetables, nuts, tofu, egss, etc.).  

For me, the downside with fast-acting insulin is when I eat a low-GI,
but higher-carb meal, thus use a larger dose (3 or 4 units).  In these
cases, I sometimes get either a mild low blood sugar 80 minutes after
injecting, or a moderate high (140's) at 2 hours after finishing the
meal.  For meals eaten after exercise, I am also prone to experience
lows from fast-acting insulin, even with a lower insulin-to-carb ratio
than normal.  For this reason, I nibble on carbs several times in the
hours following the meal.  The problem here is that the fast-acting
insulin wears off quickly in this time and if I nibble just a little
too much or too late, I get a high reading (140's).

I am still in the learning phase of using the regular insulin, but I
am hoping I can fine-tune some of these problems by knowing when I
should use each type of insulin and how long to wait before eating.
From what I have read in Bernstein's book (I do not wholly agree with
his tactics, but I believe he makes some valid points.)  It is better
to use regular insulin when you have the option of waiting 30 - 45
minutes to eat, but use fast-acting when you must eat right away or
are planning exercise 3 hours later.  Is this correct?  

Can you cover both a meal and a later small snack with a single shot
of regular insulin?  Using the fast-acting insulin, I find myself
using an extra injection to cover a mid-morning snack.  I can skip the
snack and have normal blood sugars, but still end up feeling crappy
for several hours.  To me, the extra shot is much less of an impact on
my quality of life than spending several hours feeling crappy, but I
wouild like to keep the number of daily injections to a minimum if
possible.