The HKMA has been intervening regularly lately to maintain the HKD peg. The currency is nominally fixed at 7.80 HKD per USD, but allowed to fluctuate between 7.75 and 7.85. When it hits the weak side of the band (7.85), the HKMA is obliged to buy HKD in exchange for USD. And when it hits the strong side, the HKMA sells HKD in exchange for USD.
Lately, it has been stuck up against the strong side of the band. The most likely reason for this is the large value of IPO's in Hong Kong at present. To invest in an IPO, you need HKD. Ergo there is upward pressure on the value of the exchange rate. But this will pass, as the value of IPO's in the city returns to more normal levels in due course. (Indeed, it's back down as I write to 7.7659HKD per USD).
However, maintaining the currency board is not a costless policy. In this case, the total value of HKD in circulating is increasing, which must ultimately lead to higher inflation rates.
But let's put this into context. Seasonally adjusted M1 stood at 407 Billion HKD as of August 2007 (the latest available data). Based on media reports, the HKMA's interventions so far have amounted to about $10Billion HKD, or 2.5% of the money supply. The current level of intervention would need to be sustained for some time for the inflationary costs to become large.