I use "shear tape" rather than pins on occasion. There are a few situations where it's more appropriate (some mentioned on this thread already): paper airframes that can't hold up to pins, emergency field "macguyvering", etc.
However, shear pins are usually WAY more consistent. Once you ground test, your are pretty much sure that the same amount of force applied by a given amount of bp will work every time. Not so with tape - heat can affect the tape's glue/stick, different bits of tape can have different tear resistance, an extra bit of wrap can "just enough" or "way too much", etc. Remember that you not only want to count on "x" amount of force shearing the pins (or ripping the tape) at mains ejection, but you ALSO want those pins or tape to absolutely hold against the force of the apogee event. Otherwise your mains deploy up high, which negates the whole reason for going with dual deploy. Sure you can put LOTS of tape on to make sure it holds at apogee, and then use LOTS of bp in your mains deployment ("blow it out or blow it up"), but this is inelegant at best, and very troublesome at worst.
I don't like to hedge my bets with "more than enough" bp to do the job. A little more is fine, but overdoing it is overdoing it. Too much ejection force can cause other problems. I like the consistency of shear pins over tape for this reason.
But like I said, tape is appropriate at times, and (as noted by a few posting here) can certainly work.
Either way, remember the rule - ground test, ground test, ground test.
s6