anyone have experience with working out with weighted body vests?

I'm looking for one and have no idea about them.
for example:
http://www.weightvest.com/weightedvest3.html

not sure of which weight/style is good without putting strain on my back. (I'm 155lbs) I'd rather go fairly low weight, 25lbs-35lbs? so I don't die in a 60minute solo workout. Idealy, they'd be a vest where I can adjust the weight by adding or taking away, so I can work my way up slowly...

any feedback/suggestions/experiences/recommendations are appreciated.

btw, I'll be really busy over the next few days and might not get to the thread right away. I thank everyone in advance.