I do, and I absolutely swear by mine. You can also use it for step-ups (also more recently known as "leg presses" a la Boot Camp) when your legs can handle more weight than is comfortable for you to hold as dumbbells to prevent hand, arm and shoulder strain; some even use theirs for power walking and body-weight work like push-ups, triceps dips, chin-ups, etc.
The brand I have is the All-Pro adjustable vest with a max weight load of 40 lbs. I got mine at a local (Twin Cities) Sport Mart. However, I also saw a brand in a recent 2004 Power Systems catalog (I THINK the website address is powersystems.com, OR power-systems.com) that has vests in varying adjustable max weightloads but is far more form-fitting in the trunk. As much as I like my All-Pro, in all honesty it hangs on me like a tent with armholes, and that can get a bit distracting.
Spend your money - get one!
A-Jock