Hopefully never. Free floating economy is less volotile to speculators. You start protecting your currency the big guys with more money than our annual GDP turnover start to target our reserves and deplete the reserves to fast or something along those lines. Simon you have all the technical definitions to explain better. Right now Reserve bank has inflation mandate not currency mandate.
Its just sentiment (Risk appetite, MTN/Bharti, etc). The long term fundamentals are all pointing to a weakening currency. No/low demand for our exports, dismal local economy (manufacturing/production declines across the board) and the lingering threats of inflation. When the sentiment wanes, the ZAR will weaken to R9.20 (USD) and R15.80 (GBP) based on PPP. Remember the ZAR has been a depreciating currency at a rate of 10-15% p.a. since 1985.
This tregth reaches R6/dollar again i am buy a boat load of pounds cause the reverse will ensure I get a great holiday in Europe when its back at 15:1 ;-) and I can stash my surplus in my secret jamacian account (ganga1) ;-) ;-)
Followed by 7,8,9,10 leading into 2008. Its easy to get stuck focussing on short term movements, the ZAR is probably one of the most volatile currencies in the world. If a strengthening currency bothers you that much, just sell a few currency futures.