StLouisRod:
Note I said $2000+ (that plus means, "and above")

A very nice Mame can be built for far less than $2000. Tips: Don't spend $600+ for a prebuild cabinet from ArcadeShopper and a $500 monitor, start with a Jamma cab with monitor included for half that price. That alone cuts approximately $1000 in parts. But I digress, this thread isn't really about the cost of parts, or the cheaper ways to build a Mame.
If the point is to avoid end user support down the road (which I think is important), I think I'd sell a Mame stating that no software modifications could be performed. If any were, then they are "on their own" and if things break, I will fix it by charging $75 hourly (or whatever the going rate for PC repair). Normally, I would fix any problems for free for a certain period (perhaps, a year). But if they want to go jacking around with it... I'm not going to fix it, unless I'm getting paid.
I really don't understand the temptation to do lots of "other things" on a Mame cabinet.
Watching DVDs:
I would never watch a DVD on a mame cabinet. First of all, why would a purpose-built Mame cab even have a DVD player. Secondly, why would I watch a DVD on it when the monitor is angled upwards towards the game player's eyes? It's a lot less comfortable to stand in front of an arcade game to watch a DVD than it is to sit on my couch and watch it on a real TV. And I doubt many people have a Mame game sitting in their living room/media room/etc. in place of a real TV. My wife would never let me stick a game in any room in the house other than the game room or basement! I know there are lots of people on this forum who have games in living rooms or whatever, but those are generally single/young/living in apartment types. Those are not the same people who spend big bucks on a prebuilt Mame.
Listening to MP3's/Jukebox:
I don't see the point in this either because most people have a stereo that is much better than the one in an arcade box. Even if you want an MP3 jukebox, if you are going to have people over for a party, do you want to ask them to stop playing the arcade so they can listen to music? If you must have an MP3 jukebox, it seems smarter to use your old 200mhz PC hooked up to the net and a real stereo system.
How are they going to get all the MP3s? Are you going to load 100 gigabytes of music on their for them? That'll take some time. Are you going to let them surf for music themselves? Do you really think they are going to want to take the time to dig up music on the net? I don't even bother with it, and I'm a tech type with broadband at home. Some of you already have vast MP3 collections to use at home, more than likely the people you are selling a machine to do not. (Again, I suppose you could preload it all.. but what are you selling, an arcade game, or a PC in a box?)
Other PC games:
Are you going to explain how to set up the controls for them, how to get the game to launch from the frontend, etc? I don't. Like I said before, I'd be charging by the hour for this stuff.
Frostillicus:
We can agree to disagree.

Fair enough.
As far as the microwave analogy. I'd say that using a Mame to play MP3's, surf, etc., is like using a microwave (which is meant to cook food) to melt plastic... to generate lightning from metal... to destroy household pets... etc.

If a buyer came to me and said, "Can I do this with it?", I'd tell them it is possible, but it is a lot of trouble. They can pay me to set it up, if they want. There are all kinds of things that are possible, but that doesn't mean they should be done. There are so many things that computers can do, and software can do, but most businesses don't do it, or don't install it or set it up. Why? Because it isn't worth the trouble. Because it costs too much to support it. Because it opens their systems up to virus problems, performance problems.
Rampy:
I think we are looking at it similarly. It would be much easier to be success at selling these things if they were "An arcade game that plays a thousand games" versus "A PC in a really big, heavy box, that can do ANYTHING you could ever want it to do, including play arcade games!" Unless you are charging hourly for support.

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Bottom line, if someone wants to build Mame cabs to make money, they are out to make money. Not to show the world all the great things a PC can do. If you are out to make money with PCs - limiting, reducing, avoiding "FREE" support is critical. Unless of course, your product costs NOTHING and the buyer is essentially paying for nothing but support (not the case with a Mame cabinet, unless you are charging $10k for it).
That said, it's my opinion that like most things I/T or PC related, if you want to be successful with it or not get killed by "support", you better lock it down tight. Security might not be as important as with an ATM, but I'd treat it similarly.

I don't mean to be so talkative about this, or be so forceful (I'm sure I'm coming across too strong). I just find this very interesting, and I haven't been very busy at work lately (read: bored!)

Wade