I always pronounce it ma-pa-SIMMZ, with the first two syllables almost totally suppressed.
I spent enough time in Army JROTC to pronounce it mip-sims.
I pronounce it em pee ehs Aye Emm Ess.
I don’t pronounce it. so there.
Gotta be em-pee-sims, although I’m not gonna get in a fight with ChiefScott and the rest of the SDSP (Straight Dope Special Forces).
I like M-P-Sims, long walks on the beach in the moonlight, watching small children cry, and responding to people who send me stupid emails about people putting HIV infected needles on gas pumps.
BTW I’ve never nounced professionally.
I’m with the mip-sims group… I never could understand the whole emphasis thing so I won’t say that since I don’t know
Well, I usually just spell the letters out but If you pointed a gun to my head I might pronounce it “Empty Shit” or some-such.
I pronounce it quite silly. The sillier the better.
(Although I do like “mangrove throat warbler”, phouka.)
Em-pee-sims. But often, when I look at it, I think “M-P-S (S) I-M-S, Straight Dope makes the ver-y best.”
Maybe I smoke too much.
I am with the m-p-sims group – no clue why, it just comes out that way.
Em-pee-ess-ai-em-ess . The correct way.
Bri
I can’t believe I pronounce it differently than everyone else:
“IMP-sims”
Yup, M-P-Sims for me. Odd. I’d wondered how it was pronounced, settled on that, but never thought to just ask y’all. 
Well, according to the post I made in the link Joe_Cool provided I pronounce it emp-sims, which I do. But I must come clean (I did at the NYC Dopefest I attended in April).
I never pronounced it until Demo did, and, after reanalyzing I realized that, had it’s pronunciation not have been predetermined for me, I may have been with the mip-sims crowd.
Canthearya, you are so close to the true pronunciation ::exert mind control here:: Emp-Sims!
Follow me!