its solid as a rock. its exactly the thickness of a USB connector (full size, not half) and fits great on a keychain. It's a bit bigger than the smallest ones you can find but it's good build quality and good speed.
Crucial Gizmo Jr. I keep one in my wallet with all of my most important documents (encrypted of course). It's also made it through a few times in the wash.
Most USB sticks are fairly fat compared to the connector. This makes for a slight bulge in the stash belt.