Safety First! You are better off without it if you are using up all the free space in the room. Your kitchen should be spacious and you should never feel restricted in your movement - in fact it can be dangerous if you are. Yes, a kitchen island is good to have, but not if your safety and freedom of movement are compromised to accommodate it.
If you have a big island that can accommodate many people, consider using full benches. The benches can be with or without backing to allow for more comfortable seating.
If you have doubts, you could always ask a professional designer to go over your kitchen space and make a recommendation or, if you want to save money, you could visit friends who have a kitchen islands and make the necessary comparison. Moreover, you can choose for your kitchen island to be in an L, U, or a G shape.
For those remodeling and looking for an "open" feel where perhaps the wall or half wall separating the kitchen and the dining room is taken down, a strategically placed island acts as a subtle room divider mentally separating the kitchen from the dining room but with a much more open feel.
kitchen island design layout
kitchen island and bar design photos
kitchen island design gallery