Myself, probably around 25% to 70-80%
Quote from whitster:
it depends on the setup
many of my setups are vigorously backtested, so i have no problem risking (for example) 21 pts to get a 78% chance of winning 14 pts
now, that is an unacceptable risk/reward ratio by some reckonings, but ... do the math
risk/reward only makes sense if computed in regards to the probability of that positive outcome

Quote from candletrader:
1) For my very short term trades, I often get a risk:reward of 1.5:1 (i.e. earn a smaller return than my risk)... this is because the short-term stuff is high probability (I only lose 25% of the time on the 'quick or dead' stuff)... people like Marty Schwartz and Larry Williams would fall into this category...
2) For the longer-term stuff, a risk:reward of 1:3 (much greater return than risk) sounds about right, reflective of the lower probability of a hit (a 60%'ish chance of a loss)... longer-term traders such as David Ryan and Victor Sperandeo would fall into this category...
The 'acceptable' risk vs return totally depends on the probability situation... there is therefore no correct answer... either extreme can be made to work as long as you have got the probability of losing correctly assessed...
A quick analysis indicates a lower trade expectancy in case 1) relative to case 2), but this hides the much higher opportunity factor in the former case... case 1) for me is therefore a more profitable approach...