[thejeff]

Interesting. I find the Sorceresses weak. Not bad for research and neat for the spider form, but at 1F1E1D they're not what I want to be using my one capital commander slot for. I'd buy tons of them if they were recruitable everywhere. As it is, they get bought when I can't afford the real prize.
Like most top end capital only mages, I can't get enough Black Sorcerers. They're your high end mages in most paths, your best battle mages, etc.
Since they have the Spider form, they even make decent thugs. And you'll want a lot to get the random combinations.
Since Witch Doctors have lousy research, I'll buy a couple for specific duties, but I don't want a bunch of them sitting around.

On the uberbless vs minor bless vs no bless controversy, the big spiders seem pretty effective at expansion even without a bless. You'll lose a few more, but I'm not sure you lose enough to actually slow the expansion pace. And if you're not relying on a bless, you can build researchers instead of priests in the early turns.

I haven't played with the little spiders enough to say how effective they are for expansion.