According to http://www.windowsazure.com/en-us/manage/services/web-sites/how-to-monitor-websites/#exceeded it says:
What happens when a resource usage quota is exceeded
Windows Azure takes the following actions if a subscription's resource usage quotas are exceeded in a quota interval (24 hours):
Data Out– when this quota is exceeded, Windows Azure stops all web sites for a subscription which are configured to run inShared mode for the remainder of the current quota interval. Windows Azure will start the web sites at the beginning of the next quota interval.
CPU Time– when this quota is exceeded, Windows Azure stops all web sites for a subscription which are configured to run inShared mode for the remainder of the current quota interval. Windows Azure will start the web sites at the beginning of the next quota interval.
This makes Shared Mode not practical for production sites as any one of a test site can kill all 200 sites in the subscription. But $75 per month for a "casual" site is unaffordable and not competitive.
Would Microsoft consider an Extra Small Instance option for a Standard Mode website?