It depends what you want to use it for.
I use a wireless squeezebox in my main stereo system. It allows me to keep my whole music collection conveniently on hard disc and serve it at will to my amps and speakers/headphone amp. The interface is pretty reasonable, so it's easy to use. Given that I can do all of this and be seperated physically from the PC (and any hard disc noise) , the first thing to say about it is that it's phenomenally convenient.
The music collection is ripped in EAC, so I avoid read errors that I would usually associate with a normal CD player; is stored as a FLAC file, so I don't deal with any lossy compression; and is wirelessly transmitted to the player which has no moving parts, so I minimise jitter from the player. So the technology makes it a pretty damn good transport.
It is emminently modifiable. For example, Red Wine Audio and The Bolder Cable Company produce reportedly excellent modifications for the squeezebox, whether you wish to use it as a digital transport preceeding your DAC or use the analog outs. With some relatively inexpensive mods to the player itself, and an upgrade to the power supply, many report that their squeezeboxes outperform CD transports/players costing many thousands of dollars.
It comes with an excellent digital volume control, so it doesn't require you to use any other attenuation stage. Many people report hearing their system at its finest using the squeezebox directly to power amps. In a headphone set-up, this would mean you wouldn't need a nasty pot in your headamp.
The slimserver software is open source, and there's a big community of enthusiastic users producing improvements in software and functionality all the time.
Having said all of that, if you like having your headphone amplifier/stereo system sitting next to your computer, then there's probably no advantage to using the squeezebox over a well designed USB DAC or high quality sound card. Right now, I'm at work feeding music to my Corda Aria via USB cable. I never even considered getting a squeezebox for this system, as most of its advantages are sort of redundant. But at home, the squeezebox allows me the opportunity to get truly excellent audio quality and unbelievable convenience without having to be tied to my computer. And relatively speaking, it's dirt cheap.
Chad