What are you afraid of whilst cycling

Sheldon quite concisely says:

** Airless Tires **

  Of all the inventions that came out of the bicycle industry, probably none is as important and useful as Dr. [Dunlop](http://sheldonbrown.com/gloss_dr-z.html#dunlop)'s [pneumatic](http://sheldonbrown.com/gloss_p.html#pneumatic) [tire](http://sheldonbrown.com/gloss_ta-o.html#tire).
          Airless tires have been obsolete for over a century, but crackpot  "inventors" keep trying to bring them back. They are heavy, slow and  give a harsh ride. They are also likely to cause wheel damage, due to  their poor cushioning ability. A [pneumatic](http://sheldonbrown.com/gloss_p.html#pneumatic)  tire uses all of the air in the whole tube as a shock absorber, while  foam-type "airless" tires/tubes only use the air in the immediate area  of impact.     
          Pneumatic tires require pumping up from time to time, and can go flat, but their advantages overwhelm these difficulties.     
          Airless tire schemes have also been used by con artists to gull  unsuspecting investors. My advice is to avoid this long-obsolete system.

When did he say that? Have there been any recent advances in the tech involved?

When I was a kid I had a solid rubber rear tyre on my mtb... Now that really was ridiculous!