I absolutely love my iPod Shuffle, especially since I'm a runner. I can clip it to my shirt before I go for a run and it is so lightweight that it just stays put. Also, it has an option to lock it so that the song doesn't change if I accidentally bump one of the buttons.
It holds about 1000 songs and I can play a straight playlist or I can select the shuffle option and it will play the songs in random order, which is good for some workouts because you don't get as bored when you don't know what to expect.
It has a pretty good battery life. It lasts a couple of weeks without needing a charge if you turn it off when you're not using it. However, when I do have to charge it, I need to plug it into the computer. It's a bit more of a hassle than with the regular iPod that you can just plug into the wall.
Overall, I think the iPod Shuffle is great, and I'm really happy I purchased it. The earbuds are the same as with all iPods and they stay in pretty well during a hard workout, but I prefer to use the over the ear variety because they are more comfortable for me.