Of course, I am no expert when it comes to physical training. I'm sure I have my own bad habits. And I have terrible posture most of the time- but I have the wherewithal to keep my back straight when I am working out! It is the most sensible time to be completely aware of your body and really control what it is doing. This is just my humble opinion, but when you work out on a machine you should look like this:
Granted, these are only general suggestions- I personally would have to have my hair pulled back when it is as long as that chick's, and I certainly don't look as perky and chipper as her when I work out. But the hunching over the bike or treadmill seems so, oh, I don't know...counterproductive? And so many people do it! They are going to have strong legs and broken backs. So this is my message to America- stop slouching when you are at the gym.
On a side note, my workouts have been really great lately. I have been all motivated...weird, I know. And I saw a guy last night who bore a striking resemblance to Mr. Dewey from Saved by the Bell. What more could I ask?