One of the fundamental challenges faced by adopters of a fixed or pegged exchange rate system is the loss of monetary independence (except in cases where draconian capital controls are implemented): that is, if you (a foreign country) peg to the dollar then your monetary policy is essentially at the mercy of the US Federal Reserve. Given Fed's love affair with ultra-low interest rates, this can be hazardous for fast growing economies like Hong Kong. Hong Kong is also attracting significant investments from rich mainland Chinese eager to acquire property (and establish residency in HK).
Hong Kong pursues an extreme form of a fixed exchange rate regime, typically called a currency board. (Hong Kong calls its exchange rate system the linked exchange rate system). Like any currency board arrangement, the domestic monetary base is fully backed by foreign reserves. Changes in the size of the monetary base require corresponding changes to foreign reserve holdings. While such systems are preferable in countries trying to stem frequent bouts of high inflation, it appears increasingly inappropriate for an advanced economy like Hong Kong.
Given the growing interdependence with the Chinese mainland, it makes one wonder if the better choice for Hong Kong would be to abandon the HK dollar and adopt the renminbi. As the renminbi increases its international profile and shifts towards a floating rate system, Hong Kong would be better served by adopting the Chinese currency. Frankly, it appears inevitable that at some point in time the HK dollar will cease to exist.
http://blogs.wsj.com/economics/2010/08/13/hong-kong-forced-to-fight-the-fed-again/tab/print/