ศาลาชุมนุม

I swear that I hear Thais when they are talking rather quickly pronouncing both ไหม and ไม่ as "เม". Is this pretty colloquial? I also have recordings where I hear this same usage.

Naga, any particular area of the country?

No, not really. Varies person to person. Also product to product. I've heard it used in dialogue on BP Becker's Beginning Thai CD and in recordings in the current coursework I'm studying. I can read the Thai sentences but when playing the dialogue - out comes เม for ไม่ and ไหม.

My listening skills suck, which is why I'm going back to basics and doing a lot of listening to recordings. It's just one of those oddities that throws me off.

Guess we've got our own. What Thai would know the "Jeetjet?" means "Did you eat yet?"

I reckon it's more like มั้ย than เม
I think that's what happens when people shorten a word that has a rising tone.