Wasted Office Space

With the background of continued economic turmoil many companies are looking for ways to reduce overheads.
With rent and Business Rates being two of the larger overheads faced by many companies, there has been a definite trend to occupation of smaller office premises, if at all possible.
Looking around your office now, how much space is wasted? Assuming you could do your job from home, would you really occupy the same space in a home office?