Personally, if 10% after four months is good, then the daily 0.5% that I'm making on my own is pretty freaking great. I currently have a goal, aiming for a monthly 15%-30% investment profit, but I have horrible luck too, heh. We'll see.
So what do you think? What is fair to you? Let's talk real numbers though, and not expect a 1000% daily profit. Be realistic now!

Also, what's the most that you've made in a day/month? Mine was 20% in two weeks, too bad I didn't invest a whole lot...!
Good that you know that any sites that promises unrealisable returns within a short period of time is definitely a scam.
That being said, I think the acceptable level of returns is kind of individualistic in the sense that, since returns is related to the risk, the onus is on the individual to determine the level of risk he or she is wiling to take.
For me, I a 10-15% a month legitimate investment is ok on my part although I am still skeptical on the investments sites we have out there.