This post has made me go and quickly look up the impact of the weight of shoes. This seems to be the most scientific:
''We found adding 100 grams to the shoe increased the aerobic demand of running by 1%. Now 100 grams is about 3.5274 ounces, so each ounce changes the cost of running about 0.2835% (1/3.5274= 0.2835). If you can run a mile in 5:40, that is going 284 meters per minute and that speed of running typically coasts about 55.55 ml O2 per Kg body weight per minute. 1 less ounce will change the cost to about 55.7075 (from 55.55 above) and that VO2 will be associated with a running speed of 284.7 m/min and a mile time of 5:39.17, so about .83 seconds for a mile, per ounce less weight."
Source: http://runsmartproject.com/2012/02/06/how-much-does-shoe-weight-affect-performance/
Ha! So bascially stop blaming the shoes and run more. Fair enough.