If efficiency and time are not a great concern, and there aren't a lot of hills on your route, then a beach cruiser would be fine. As the above poster suggested, give it a go on a weekend. That'll give you an idea of how long it would take you and whether you want to do it at all or not. Plan to spend a little more time on the actual ride to work though, because there will be more traffic then and it may slow you down. Unless it's all a multi-use path through a ravine or a park... then you'll be faster, because fewer people will be on the path.