Lots of parents would consider a cheerful time-out successful. You still have interrupted the undesirable behavior, your son has had a consequence, and he realizes he wants his mommy to be happy with him (hence the smile). The point is getting him into a new mental space where throwing won't feel necessary to him, more than punishment for punishment's sake.
Be aware that timeouts simply do not work equally well for all children. Nor does spanking or any particular discipline. Depending on the child's personality, the dynamics between parent and child, and how the child interprets any particular discipline, you might get great results or just the opposite. Some kids will contemplate the error of their ways during a time-out, while others will seethe while plotting revenge.
If you want to continue trying time-outs, consider finding a new spot for your son to sit, or leaving the room. Set a timer that he can watch count down, and tell him he can get up when the timer rings. That should both take his focus off of you and begin giving him a hands-on sense of time. If he gets up, put him right back, but don't keep resetting the timer – that can change the whole issue from his original misbehavior to a new and escalating power struggle. Just use the time-out to interrupt his play for a minute.
Check out http://www.askdrsears.com/topics/discipline-behavior for many useful discipline techniques. I also love Dr. Harvey Karp's technique for letting a child know you have really heard his request: http://www.youtube.com/watch?v=fJ1428uYs2g&NR=1&a...
ADDED: I've been pondering what I used to do with my daughter after a time-out or other discipline. I didn't know what she actually understood if I just asked her "Do you understand?" The correct answer is, of course, "yes," and so the child may learn to just say that. But a better question is "What did you do that was wrong?" Then you find out what the child knows. And even better, follow up with, "What should you do next time?" If he doesn't know how to express frustration and upset verbally, teach him the words. "I feel mad/bad/sad/frustrated." That alone can begin to make a difference in a child's chosen behaviors. They really want to be understood.