Awesome, awesome, awesome. I too, like many other reviewers, started out with a huge, bulky case for my 80GB iPod w/video. It was so-so, but kind of annoying, especially having to remember to clean and dry the case and armband after every swim, and be extra vigilant when sealing the thing (making sure there wasn't any debris on the o-righ seal, etc) This thing on the other hand, is amazing. It's absolutely tiny, and with a good pair of UW headphones (just get simple earbuds and tuck them under a cap...no UW headphones will work 100% of the time without a cap, due to drag and the necessity of having a solid, watertight seal maintanied at all times for functionality. So just accept that you have to wear a cap to use any UW headphones for lap swimming, and get the lowest-profile earbuds you can find. I got the ones from Aquapac) your entire UW music system can be attached to your head without noticing it at all. There is zero weight with this system, and the drag is negligible. The construction is very solid and the clip attached to the back is perfect for clipping to goggles or the cap itself. (I recommend goggles for comfort. The ONLY downside I can see to this is that it's so small you might lose it if you are careless with it while not attached to earphones, but that's your problem not the iPod's. This is especially true if you take it into the ocean and ride waves with it. But all-in-all, this is the way to go.
And even though it's not that cheap, think of it as an investment in an all-weather mp3 player, not just an UW mp3 player, because it is a fully-functioning iPod shuffle that can be used anywhere, anytime. It's just also fully submersible as well. So you can do all manner of exercise with it (run, bike, row, ski, swim, surf) And not only is the waterproof feature awesome for swimming, but it makes it impervious to sweat for workouts, and accidental spills also. When you factor in how much an underwater case is going to cost for you current iPod, the weight saving and convenience of this tiny little unit compared to bulky cases, and the possibility that even with a bulky case you may flood your iPod anyway and ruin a $400 device in the process, there really are no drawbacks to just buying this instead. I wish I had just bought this thing outright in the first place. Buy one.