Imp force-cast macros

This is something I haven't touched on previously, but there's been a lot of talk about it for some time on Elitist Jerks, and it's spilled over to the class forums lately, so you've probably heard about it.

Supposedly, it's a DPS gain for destro to macro /cast firebolt onto all of your other spells, thusly:

/cast incinerate
/cast firebolt

/cast immolate
/cast firebolt

And et cetera. So, what's this all about? Is it really that good? Read on in the break.