That's why I have bought a big flat recently and wait to sell my small flat. It is fact that rental has been going up recently and more expensive as HK Government imposed tighten housing policy since June 2011. it makes less people buy flat and they are going to wait the overall property price dropped. It will create another problem on big jump on rental. Also, landlorad will pick the good tentant to rent too. My good friend has the similar problem when his rental contract expired on coming Aug 2011. His landlord increased around 25% on his new contract.
Anyway, interet rate will not up too significant as HK dollar was pegged with US in short term. In the long run, owning a flat is better than renting a flat.