While developing you may come across the issue where after multiple calls (normally 10) to your WCF Service hosted in IIS, further calls simply "hang", with the debugger not really giving you much clue why. By default the limit on multiple concurrent connections is as follows...
Windows Vista Home Basic - 3
Windows Vista Home Premium - 3
Windows Vista Ultimate - 10
Windows Vista Professional - 10
All Windows Server SKUs - Unlimited
Calling Close() on your proxy class instances is a must to avoid this from happening.