According to The Bicycle Helmet Saftey Institute, helmets that come to a pointed rear end put you at risk of "snagging" on something if you fall.
It sounds like rear pointed helmets are yet another attempt to emulate racing styles. But if, say, you were sliding forward at 30 mph on your back and your helmet snagged...you could come to regret being so stylish.
The institute recommends a helmet that:
1. Meets the CPSC bicycle helmet standard.
2. Fits you well.
3. Has a rounded, smooth exterior with no major snag points.
4. Has no more vents than you need. More vents = less foam.
With all that in mind, I picked up a Bell Variant (below), to replace a worn out old helmet. Apparently, the life of a helmet is about 3 years. Once any part of the interior foam breaks the helmet is close to useless.
Helmets are seldom seen in Europe, by the way.