Being Ill and Workouts

Everyone hates being ill, but i think the keen 'fitness freaks' hate it even more. There is nothing worse than waking up on your workout day, to find yourself feeling like you've been hit by a train! So, is it okay to workout even if you are under the weather?
Over the last couple of weeks I have started getting back into my workouts after a 5 month lay off, and this week I have had quite a bad cold (every guy knows man flu is deadly!). I did manage to get a workout in yesterday morning, and it was the afternoon that the cold decided to set up camp! If i'm honest, i didn't go 100% in the workout, and I think that was because It was the start of being attacked by man flu!
I have read many things about workout out and being ill, and it all depends on how you feel. If you have 'minor symptoms'  such as a sore throat/runny nose, then it is okay to work out, but just not at your maximum tempo. However, if you have symptoms that are much worse ( i won't name them just in case my readers are eating!) then it is best to rest your body for a couple of days and then get back into your workouts.
It comes down to common sense I think. If you are feeling so bad that you feel like you have been the punching bag to Mike Tyson and David Haye, then I don't think its wise to workout! Judge yourself by how you are feeling, but if you are suffering from a few minor symptoms then it is okay to have a moderate workout.
Hope this helps!