Antisense has always been a great idea that hasn't worked out as well as theory would suggest.
But beautiful theories always get murdered by ugly facts. (This is meant to be humorous.)
RNAi runs many of the same risk (stability, delivery to the appropriate location), but seems to require a lower dose to be effective.
It is interesting that the antisense and RNA companies, such as ISIS, RNAI, and ALNY are still in the running when it comes to licensing intellectual property.