I am planning to do a mobile project using the OLinuXino board, so I am considering powering it directly from a Li-Ion battery instead of using an adapter or USB power. I wonder if anyone has tried this. Do I need to add any protection circuit or charging, and will the performance be affected much?
This is fine. Performance won't be affected. No need of adding anything just make sure that you use the Li-Po battery connector and double check + and - markings on the board so you don't connect the battery in reverse. The connector is not standard and it is possible to short-circuit the board if you don't ensure + of battery goes to the + connector on the board.