Hi Nik,
Depends what your definition of expensive is. Much cheaper than spending around £1000+ getting a equivalent quality stero system that is digital compatible. Also for £200+ you can buy an 80GB IPOD that will fill up. For £100 I have access to music on a 320GB hard drive that I can upgrade cheaply to an even larger one if I ever collect enough music!!!!
It gets hung about once every blue moon as the latest software update has just about sorted that out.
How can such a gadget become obsolete?
As long as it streams music from a PC to a music centre then either the PC has to become obsolete (as an item not just the one you own) or the music centre. Latest software update is Vista compatible so that is compatiblity even if you buy a new pc now. Stereo is no problem as long as you have some form of external input. If MP3 / WMA files all change then we are all buggered!!