Single speeds will tend to be a gear that you must always turn, and can't freewheel. It takes a bit of getting used to, and if you do try and freewheel, you are very likely to end up going over the bars. Stopping is as easy as a bit of back-pressure on the pedals, but make sure you're sprocket at the rear is tight otherwise this might loosen it off, and you might freewheel after all, and now with no way to stop. Some bikes do have brakes for road use though, but it will still take quite a bit of extra distance for slowing, and I recommend pedals and cleats for this.
Of course, this can be disregarded if the rear wheel has a freewheel hub and sprocket.
Acceleration is a bit harder as its a gear for speed too. It would be a bit like starting a car in 3rd. Takes a bit to get going, but once you're away, you can trundle along at a fair speed.
Maintenance is a lot simpler, theres less mechanical parts to break. They are, of course, cheaper due to the lack of components but as they are becoming "fashionable" for commuters so prices are going up a bit.
Whatever you choose to do with your bike, make sure it fits though, and its right for you. But most importantly, enjoy it.