I tend to tie my hair into a ponytail if I'm going to an interview (since some people think it looks neater in a ponytail and I'm the one wanting the job, I may as well tie it back).
I won't tie it back for a wedding/funeral etc though. Anyone shallow enough to care about my long hair probably wouldn't invite me anyway (and I wouldn't want to go!).
I think the brown suit in the Akercocke picture goes much better with long hair than a black one. Probably because it looks less formal than a black suit with a white shirt. The guy on the far left looks a bit like me.
Bavarian Motor Works
No, doesn't look like a gentlemen at all.
Styles change. Historically, having long hair showed that you were a gentleman -- that you had time to keep it clean and styled. Soldiers had to have short hair to prevent lice, and after the large wars the style spread to everyone else. In some cultures cutting a man's hair off was a punishment, or could be used to show a man wasn't free (e.g. soldier or slave).
Herman Lee from Dragonforce..... now that's a man with long, long hair to die for! I went to a concert of their recently and I was in the front row staring at him...