I use them as soon as I see them. For me they aren't worth carrying around to be used when I really might need one, and early on when I might in theory have use of one inventory space is too limited to keep anything extra on hand.
Hahaha. Maybe it was implied? Perhaps I inferred... Either way now SittingDuck can see it's still out there in the code to possibly be brought back by TFP or an industrious modder.
Some seem to say it was never there. I do remember it was around at least in creative in b197 and maybe b199. Best I can tell this is the xml code for it.
<block name="flamethrowerTrap">
<property name="Extends" value="dartTrap"/>
<property name="CreativeMode" value="None"/>...