well, 30lbs is the max, so they'd be great for arm and shoulder work.
but you'll quickly outgrow them for back and chest exercises.
they have PowerBlocks and Weider (or was it soloflex?) puts out a similar set that you can even buy at Sears and Scheels.
They aren't bad, and would get you by for a while...eventually you'd need to add more weight, but would continue to use these for certain isolation exercises.
This is why I personally prefer the gym. They have all the various poundages I could ever need, and its $10 a month. May not be what you're after, but if joining a gym or the YMCA is a possibility, you might wanna check it out just in case.