I'm a morning work-out person. I think it's a great way to start the day, and it boosts your metabolism, which means you burn more calories throughout the day (bonus!).
But the other day, I got home really late from an event, and I knew I wouldn't be up for going to the gym in the morning. But I had skipped my work-out the day before, so I HAD to exercise at some point. So I went to the gym after work. I realize this is not very strange behavior: plenty of people go to the gym after work, and they probably think I'm crazy for waking up at 6am to hit the gym. But for me it was odd walking to the gym during rush hour traffic.
I did enjoy myself though! I didn't do a very hard work-out, just my usual cardio and an ab circuit. It felt just as good to end my day with a work-out as it does to start the day with one. So, even if you have a normal exercise routine, it's okay to mix it up when your schedule gets a little hectic!