The following is shamelessly nicked from Amazon (Who probably nicked it from Logitech themselves)
Enjoy the elegant styling and premium sound of Logitech Z-4 speaker system, featuring a modern, home audio inspired design and advanced driver technology. Award-winning pressure-driver subwoofer technology delivers unparalleled distortion-free bass. Sleek satellites include durable cast-metal stands and feature one active and two pressure drivers, producing the high-quality sound you expect from Logitech. The convenient wired remote control includes a headphone jack, auxiliary input, volume, subwoofer, and power controls. Setup is easy with color-coded audio cables.
I bought these speakers on Saturday to replace some generic 2.1 set and I can safely say they are fantastic, great clarity, decent bass (Which is controllable on the remote control provided, perfect for when thumping bass is not appropriate) and is well worth the cash.
Oh, and they look pretty good too, well, I like the look of them, and in my view are well worth the extra £10 to step up from the capable X-230s.
Edit: For reference, the next cheapest is Amazon at £49.59 delivered.