I've had an OS X (Hackintosh) cab up and running for the better part of a year now, and used a Mac Mini at my TV for MAME-ing for over a year before that. My findings:
MacMAME is indeed dead, which is a shame, as it had the most Mac-like and intuitive front end. Still usable, but it has quirks, and it's obviously long out of date in terms of MAME versions, so a lot of MAME features aren't available (i.e., overlays and backgrounds, many video controls, etc.). The OS9 version is still a great emulator for classic games, particularly vector games. Since MacMAME predates Intel code, it won't work at all under Lion, unfortunately.
MAMEOSX is also dead, and also has quirks, mostly related to recognizing multiple USB controllers (I still can't get it to recognize the spinner on my CP, for instance). But it was a very nice project while still around. I'm told it doesn't play well with Lion, but then again, Lion sucks.
SDLMAME works great (assuming you settle on a front end), is up to date, and has a ton of nice features. Not exactly "unpack the installer and drop in your Applications folder" as far as setting it up, but you don't need a degree in computer science, either.
http://sdlmame.parodius.com/Front ends for SDLMAME:
EmuLaunch is the simplest and most usable in a cab environment, since it's explicitly joystick-selection-friendly. Takes a little tweaking to set up (make sure you select SDLMAME as your emulation engine), but worth the effort, even though it's technically a dead app.
MAMETunes is a neat frontend, simulates the iTunes interface. Not my favorite for various reasons, but I can see why people like it.
MAME+GUI (aka M+GUI) is probably the most versatile Mac front end, and the one I use when I want to dig deep into the recesses of MAME (I have a much more limited ROM set for EmuLaunch, only a couple hundred games). It also plays very nicely with SDLMAME. Not particularly cab-friendly, though.
I tried MAME Library a while back and liked it, but it didn't play well with SDLMAME. Don't think it's been updated since, when I emailed the dev last year he said (nicely) that he didn't have time to debug the SDLMAME section. Hopefully he'll pick it up again one of these years.
There are a few others, and you should experiment around to find the ones you like.
Regarding iPhones and iPads, you have to jailbreak to get true MAME going on them (unless you lucked out in the iMAME sweepstakes recently). MAME4All is the app if you do want to jailbreak. I hear it runs great with iCades.