I can't imagine anything with more than something like 12% annual interest being legit. But most of these things offer interest rates that are so insane that it's not possibly legit.
Just take a look on this one, for example : Remi Trade. Look at the up left corner, and click on a date. You'll see the daily results of their trades, and the % of benefits of the days.
This HYIP is born months ago (maybe years? don't reallt know) and is one of the safest actually. We can't never know if this is real trade of fakes one... we the only sure things is that they are paying for months.
You don't earn any profits the weekend, because they don't work. So, that's said, you can expect 5-8% weekly. It's much more than your 12% annual interest, ok. So you will probably don't trust them. Whatever... there are some opportunities in HYIP to earn money, and to loose money. The real question is how to choose the best plans and don't enter in fakes one. That's the only key to generate profits.