I think likeable can equal being pleasing to the "lowest common demoninator", or least likely to offend the most number of people, which can hinder as well as help.
I spent years flatsharing and the more people you had in the house, the greater the chance the 'likeable' person you pick from the selection process is going to end up being highly flawed/annoying/unsuitable flatmate, because of the LCD theory - you actually aren't looking for the best person, but the least offensive/most 'on the surface' likeable person.
Personally I quite like people who aren't afraid to be a little offensive/shady/themselves. People who try very hard to be widely liked are a pain in the ass IMO & therefore not very likeable. Other people have genuinely charismatic personalities and attract people to them.
In my industry (music), some of the most annoying/awful/arrogant/self centred/seemingly unintelligent tossers you'd ever be unfortunate to meet do very well. Then some quite nice people do well too.
So I agree with hully - it can be an asset, but isn't necessary for success.
I think being blessed with charisma will do you better than being 'likeable'.