You might want to check out Slim Devices (acquired by Logitech now) - http://www.logitechsqueezebox.com/how-it-works/overview.html.

I'm usually not a big fan of all-in-one solutions from vendors like Logitech - but this is a no-brainer. If you have a NAS, you can hook it up, and control it from any web-enabled device (computer, android phone, iphone, netbook, maemo, ...) throughout the whole house over wireless. There are remote controls that work over a wireless network (Duet controller), and they also got speaker+player combo's.

The software is free, and available for Linux and Windows (no Mac I think?) - and it scans your library you point it to, indexes pretty neatly, and sports a good search, shows new music added ...
Also - same system streams internet radio, and there are a lot of plugins and small apps available (alarm, multiroom vs. synced audio stream, ...).

In my setup, I hooked 5 players up over cable in the rack closet, which are connected over audio cable to separate amplifiers. Speakers in the ceilings are connected to those amplifiers.
My rooms stay clean and uncluttered, and I control the whole thing through my HTC Hero phone, and the misses through her Iphone. The navigation and lookup on all devices (webinterface, phone apps, duet controller, Nokia 770) is pretty quick - given that I run an MP3 library of around 60Gb.

To pass the wife test - you can try and set up one of the products they have, and expand later on.

Total cost, without amps or speakers - 5 rooms, 5 different streams --- 5 players, 1 Duet controller - around 750Euros (around 1000$, approx).
However - if you'd only need one room to be connected to the NAS over wireless - you'd be set with about 400$, I guess (Duet controller + player).

When clients or friends are curious about the setup - I just give them the Duet controller or the Maemo tablet, put them in one of the rooms that are kitted out - and let them have a go at it. Even the n00bs or the laymen understand it without any info, and are quickly listening to their own stuff ...

Just my 2 cents ...

I was looking for precisely a tablet like this, to use as a remote control for my domotics and home automation.

Every inhabitant in my house will be getting a Nokia 770 - which can then run Flash apps on the 770, thus controlling the whole house as such. This gives me the ability to code my own apps in Flash - store them on a centralized server, which can then be used by each family member.

I use Vantage [vantagecontrols.com] devices - as they have an IP enabler that allows to match a local IP to each button, sensor, or whatever thing you incorporate. The frontend is Flash - enabling me to use any computer or flash capable device to run the show.

Now - if I would have wanted touchscreens in each room, that would have set me back around 1000 euros per screen - which I thought was ridicully expensive.

The Nokia 770 enables me to do all this however - and a ton more --- browse, read, etc.

I think the 770 has a bright future, albeit not for the sales drones and their ilk - more for the DIY homeowner or traveller ...

Just my 2 euros.