Interesting. I am not really current on the cost of what the "advanced cash registers" (i.e. non windows) are going for, but I was under the impression they were kicking out 3 terminal systems for 7-8k, which is quite a bit less than what most of this second or first tier windows based systems are going for. I have run into a few in the bidding process (not very often though), and at that point, I usually start to get a little skittish because I figure the prospective client is buying mainly on price- or just isn't interested in the bells and whistles they will get with more advance stuff. I am sure I lose sales over it, but I am not one to talk one out of restaurant owners out of what they want because of the nature of this business. When you sell a system you end up with a client for 5-7 years whether you want them or not, and I would prefer to not have them resenting us because they over bought and don't see the benefits.
As TLowder suggested- I think the architecture in terms of how it's designed and what database it's using have a huge impact on it's performace and stability. That's actually one of the draw backs in ALoha, IMO. There is database info on the front of house terminals, which creates a lot of network traffic and communication- as opposed to say, systems that simply have a short cut running to the back office, where most of the processing is done there, similar to "dumb" terminals.
Aloha-on the front of house terminals will unofficially run on well on Windows 95 on up. I systems with W98SE-XP seem to be the most stable. Back of house wise, I have been pretty happy with XP. XP across the board is probably your best bet though.