I've just restarted 30DS, i only got to level 1 last time but going to get through it all this time around. I know from when I did it i noticed a change in inches rather than weight, this seems to be the case for quite a few people though some do manage to shed pounds. Some people find a small jump in the scales when the start (water retention) i'm not weighing in for a while so I can't tell you if its happening with me.
As to the 20lbs thing, nah dont think so BUT i have to say this is one of the most challenging things i have done (not done a lot to be fair) people who are very fit may not struggle with it as much as i have but it is absolutely worth every single second. You will see a change in your body I think i have only ever sen two posts from people who felt it didn't help them.