Ah! I haven't been here in a while so I didn't see this thread. But this does explain the sudden surge of e-mail about this topic.
Here's my take: I think MAME OS X is great, and I gather it's only going to get better. I'm more than happy to help Dave out with this as needed, and in fact we've talked about it some in the past day. I have to confess I haven't yet run MAME OS X or seen what it does aside from glancing at the webpage (not to mention my ROMs are horribly out of date) so I don't know a whole lot about it.
As for MacMAME, well it's my baby and it's hard to kiss it goodbye after 10 years so I'll likely never say "it's dead." In fact, I continually entertain the notion of reviving it. I've kept personal builds going for a while now and I got close to releasing an update for the 10-year mark but I just can't seem to scrape together the time to polish it off. I had some thoughts about doing that once I relocate to Cupertino since I'll be awash in free time for a while, but there's no strong motivation. MacMAME's biggest plus is the integrated front-end, but it's way too "Classic" MacOS nowadays.
From a development standpoint, I'm not entirely convinced that MAME is best served by Cocoa, particularly with the event-loop inversion but I could be very wrong and I don't want to get into a Carbon/Cocoa flamewar, particularly since Apple has already delivered a few critical knife wounds at this latest WWDC that make the topic mostly moot.
I'd like to do some performance metrics pitting MacMAME against the Cocoa core in MAME OS X and to experiment a bit privately, but that's probably about as far as it'll ever go. Carbon's ambiguous future of course really makes any public release of MacMAME doubtful, because a switch to Cocoa in MacMAME would be wasted effort in light of MAME OS X. So it's almost a 95% certainty that it won't see any future updates. In fact I'm happy about the prospect of helping out on MAME OS X where I can and not having the burden of managing the release. I always found that very stressful because I had a compulsion to be very hands-on in the forums immediately following each release tracking support issues.
So enjoy MAME OS X and use it with my best wishes.
If you have strong opinions about my continuing to do something on MacMAME, feel free to comment. If it does go forward at all, my preference would be to make it an unsupported "secondary" MAME app on the Mac with MAME OS X being the standard bearer and I would of course alter the webpages and MacMAME docs to mention that - if they ever get updated again at all.