You exercise your thighs more than on a normal bike. Be prepared to feel sore muscles in different areas than before. Although gravity doesn't help you pushing as much as in an upright position, my feeling is I can push more aggressively as the thighs are engaged more. Aerodynamics is a real speed boon.
I would not cycle them to work for various reasons: higher chance of theft, the upright position helps in seeing and being seen, and the longer "hood" of recumbents means that more bicycle is ahead of your eyes which means you'll have to slow down more at a multi-way stop before making sure no one crosses your way.