skydriller - now you know! The oil industry certainly knew about the false alarm issue, not quite so sure they knew about the mutual interference issue. But don't forget, those in the oil industry making such decision often have no understanding of aviation, and the lobbying power of you guys is perhaps higher than you think.
As you say, the answer is a cleverer device - one that does not suffer false activations nor interfere with the "proper" beacons. Until that device exists, lets keep them off the aircraft!
There are (were) at least 3 different designs of PLB in use offshore, I use the term "wristwatch" generically.
Can't say if GA PLB cater for this issue or not, it would probably depend on the model. Fixed ELTs have the advantage that they are normally activated by a g-switch - ie automatically in the event of a crash whilst you are unconscious. Portable ones will work after the aircraft has sunk, provided you keep the aerial out of the water and are in a position to turn it on. So I suppose it depends on where you intend crashing!
Perhaps the opitimum is a fixed elt with a crash switch, that can be unclipped from the airframe and carried off by you.
HC