Are these things any good?  I plan to ride to work and back often and the heat hear is unbearable much of the time in the summer.  I have a full helmet with face shield but it gets pretty hot inside even with vents.  

How many use the half helmets and for those who do not let us know why?

One would think thet half would not protect as good as a full, but is there any data to support this.  

I don't, and never will. Several years ago, I dropped the bike (low speed) but, the spot on my head that would have received the impact was the right occipital lobe. Feel down to the base of your skull in the back, then find that spot where the skull kind of goes up before it meets the spine.
That was the point of impact I had, and a shortie wouldn't have protected my noggin.

Helmet went out in trash next day.  

I will always wear a full face.  A friend had a catastrophic failure of his drive shaft that locked up the rear wheel.  Sent him over the handle bars and landed face first on his helmet.  He slid on his face, the front of his helmet was scrapped beyond belief.  With out the benefit of a full face helmet, he would have no face left.  

Ouch!  I use a full face now but have a half helmet.  I'm thinking full face for my passangers and half for myself when I have a rider or when its real hot.

It's gotta beat no helemt at all and I love riding without one though I do plan using one most if not all of the time.

Quite a few people in my area don't wear helmets at all.  One guy I work with even says if he was wearing one in his crash it would have done more harm than good.  I doubt that.  Kind of reminds me or "loud pipes save lives" saying.    

I think of myself as pretty safety conscious, but I go with the half-helmet in the summer.  It is so freaking hot here.  I wear a full face as long as I can bear it, but when it is consistently in the 90's, I just cannot pull it off.  Especially when I have a jacket and kevlar jeans on.

It is a bit better than wearing nothing...  

That's what I'm thinking.  I already have Hyperhydrosis (profuse sweating) around the hairline. The rest of my body doesn't perspire so much, so other gear is not a problem.  

I am not a big fan of half helmets. I was also in a motorcycle accident and I went from 70mph to 0 in 50 feet and if I was wearing a half helmet I would be digging dirt out of my face and most likely either be a vegtable or worse. I still have the helmet and keep it as a reminder it saved my life. But this is a free country so every rider must decide what to wear as far as helmets.  

So,
If it were possible to keep your heads cooler on the hot summer days, would you wear a full face helmet?
This is an anyone can answer, I'm trying to gauge something.  

I would welcome a way to stay cool in the helmet on hot days  

frbock:
So,
If it were possible to keep your heads cooler on the hot summer days, would you wear a full face helmet?
This is an anyone can answer, I'm trying to gauge something.

All day long...  

I often wonder why a bike riding engineer hasn't come up with miniture fans or internal cooling systems for helmets???  

I have the same bike and the same question.  What does everyone think about taking off the face shield of a full helmet and using eye glasses?  

Lots of riders choose not to wear a helmet at all, which I would say is extreme . Many riders wear full face helmets , body armor, Boots gloves etc. and seems extreme the other direction . Certainly everyone has the right to choose and to a degree depends on your riding style .
I'm moderate in my approach to safety equipment , always wear good boots, gloves and helmet to ride . But it gets real hot here in south Texas and many people wear half helmets for cruising an touring .
It may well be a compromise but some protection is better than none at all.  

Hey, osun, I found the mesh jackets are actually cooler in the sun than riding without. They block the heat, and the wind from riding gets rid of most of it before it gets to your skin. If you get caught at a crawl, it's payback time.

Everybody else... I have an idea. I need to do some math.  

I received my half helmet and will wear it at times though I did  try the full face without the face shield using safety motorcycle glasses and it is much cooler.  

I don't see a problem with this as the face shield doesn't appear to offer any protection in a crash.  You are taling a chance of getting hit by road trash without the shield.  I also ordered a tinted shield for my half helmet.