I've had the swimp3 v2 player since December 2008 and have used it around 5 times so far on particularly long distance swims. It really does work well once you get it into position.
The ear pieces clip onto your goggle straps and sit vertically just over your temples - right in-between the goggle and your ear. Once I'd tightened up my goggle straps, the system stayed in place and enabled me to do 1500m sets without having to stop to adjust it.
There are just three buttons to operate the device - on/off and skip forward/back which also doubles as a volume control. This means that you can quickly and easily control the device, which is important when you can't see what you are doing.
The sound quality is impressive given that you're in a pool, thrashing around. OK it's not quite like sitting on the bus listening to your ipod through sennheisers, but it's not far off. The sound has more treble than you'd usually go for, but you can hear the tracks clearly - fyi I've been enjoying the prodigy, radiohead and coldplay mostly :) - and the unit goes up to a high volume without distorting.
Battery life seems good. I've plugged the player into my PC twice so far for a few hours, and have had 10 hours uninterrupted playback. There is no battery life indicator though, so I guess it will cut out on me one day just as I'm warming up!
The only other negative things I can add are, one - the player did not recognise my WMA tracks (i dont know why), so I've been restricted to mp3s instead, and two - the player seems to play some of my album tracks in the wrong order with shuffle mode both off and on?! These two things are annoyances but don't distract from the fact that this is a neat little unit which enables you to swim unhindered listening to your favourite tracks, which is incredibly motivational!