You’d forget you were wearing it if you didn’t have earbuds in, so it’s a fantastic running or gym player. A lot of bells and whistles for something so small, including a stopwatch (with lap timer). Also: FM radio, voice recorder, microSD expandable storage, and it plays all of the major audio formats. Easy to drag music onto it via the Mini USB port. Decent sound (if you have some decent earbuds). Excellent battery life. Cheeeeap.
If you shake the Sansa Zip, something rattles a little inside. This probably shouldn’t happen. When you’re running, the small (1.1 inch) low-res screen is very hard to read, and it’s quite dim which makes it pretty bad in bright sunlight. Not waterproof/sweat-proof. (Why not? It should be.) Its tiny processor is pretty wimpy — tinkering with the stopwatch while listening to music caused my track to skip. (Right in the middle of Busta’s flow. You do not do that!).
If you don’t mind using your phone, then don’t bother. The 8GB one doesn’t make much sense to me: just get the 4GB model and grab a cheapo micro SD card so you can put more music on there. Having a dedicated music player for working out is not a terrible idea, and the Clip Zip’s lightweight, cheap factor and other features make it a pretty decent one.