I had fiat sitting in MtGox and just today I decided it might be a good idea to convert a substantial part of it to BTC. I still keep a part in fiat, just in case the price goes much lower and I want to buy more at a lower price.
You might ask if I'm sure that the price will go up again. No I'm not. And I really don't know what will happen. My gut feeling tells me my decision is right. Let's see.