Having used Plantronics 550 headsets for the past few years, the only gripe being the volume / mute button breaking with prolonged use, I decided to try the 770 set.
Different design, much updated, they are designed to allow you to hear what's happening in the room around you, and still get great quality sounds from the headphones. It does what it claims, you can indeed hear your surroundings very well (no more missed phone calls), but this does sometimes make the computer sound a little distant and with a 'cave like' echo, but it is a small difference and you soon get used to it (as compared to the 550 which cover the ears closely).
The manufacture of the headset is good, they are large cups with a velour padding that completely encase the ears. The head strap is connected to the cans elastically, so there is no need to 'adjust' to fit head size, the wires look a little skinny, but seem tough - the durability of this suspension arrangement only time will tell. I haven't got the 'surround sound' to work yet, need some digging on the internet, but I'm using their USB key rather than a dedicated sound card, which may improve results.
The microphone is solid, and works a treat - no digital filter this time, but sound quality seems comparable to the 550's. Overall an impressive, extremely comfortable and very very useable headset, a great improvement on the previously unsurpassed 550. The volume switch and mute button on the cable is now a dial and physical switch, which should be more durable. Overall very good value for money, but be aware of the slight lower quality sound due to the ability to hear your surroundings.
Plantronics Audio 770 Surround Sound Headset