I didnt realise the concept had a name (IBO) but bounties have been operating as a very useful tool for some considerable time in crypto. Look at the ANN pages here on BCT for ALT currencies. The first questions often discussed are bounties. People are prepared to do tasks and bet on the currency of the coin being offered.
So IBO is just like bounties? Makes sense, since it is a short form of 'initial bounty offering'. Yet I am not sure whether bounties are always about skills. I have seen bounty threads asking one to join one's computer to mining pools. At the same time, ICOs may ask you to do something instead of paying money to get their coins as a reward. A rather common situation is when ICO campaign asks you to translate their official info into your native language and they pay you in their coins when they are released. That's why I guess this ibo and ico things don't differ that much and there isn't much sense in distinguishing them.